LEAD OXIDES, COMPOSITIONS COMPRISING LEAD OXIDES AND METHODS OF MAKING LEAD OXIDES

Abstract

A composition is provided comprising one or more of alpha lead oxide, beta lead oxide, metallic lead. Pb.sub.2O.sub.3 and Pb.sub.3O.sub.4, the composition comprising particles comprising sub-particles, the sub-particles having a mean greatest dimension of from 10 to 300 nm. Methods of making such a composition are also described.

Claims

1-18. (canceled)

19. A method of making a composition comprising alpha lead (II) oxide, the method comprising: converting lead citrate into lead carbonate by heating the lead citrate in the presence of an oxidising gas and carbon dioxide, converting the lead carbonate into PbOPbCO.sub.3 by heating the lead carbonate; and heating said PbOPbCO.sub.3 in a substantially inert atmosphere.

20. A method according to claim 19, wherein the PbOPbCO.sub.3 is heated in the substantially inert atmosphere for at least 5 minutes.

21. A method according to claim 19, wherein the PbOPbCO.sub.3 is heated in the substantially inert atmosphere at a temperature of from 300 C. to 400 C.

22. A method according to claim 21, wherein the oxidising gas comprises molecular oxygen, and the molar ratio of carbon dioxide to molecular oxygen is at least 15:1.

23. (canceled)

24. A method of making a composition comprising beta lead oxide, the method comprising heating lead citrate in a flow of a gas comprising an oxidising agent, the method comprising mixing a precursor gas comprising the oxidising agent with an inert diluent gas to provide the gas comprising the oxidising agent, wherein the molar ratio of the inert diluent gas to the precursor gas is at least 1:10, and no more than 3:1.

25. A method according to claim 24, wherein the lead citrate is heated while exposed to the flow of gas to a temperature of at least 250 C. and no more than 450 C.

26. A method according to claim 25, wherein the lead citrate is heated while exposed to the flow of gas to a temperature of from 275 C. to 375 C. for a duration of from 60-180 minutes.

27. A method according to claim 24, wherein the oxidising agent is in the form of a gaseous oxidising agent, and the gas comprising the oxidising agent comprises at least 5 wt % oxidising agent, and no more than 14 wt % oxidising agent.

28. (canceled)

29. A method of making a composition comprising red lead, the method comprising: converting lead citrate into lead carbonate by heating the lead citrate in the presence of an oxidising gas and carbon dioxide, converting the lead carbonate into PbOPbCO.sub.3; and converting PbOPbCO.sub.3 into alpha lead oxide and converting alpha lead oxide into red lead, by heating the PbOPbCO.sub.3 in the presence of a flow of gas comprising an oxidiser at a temperature of at least 350 C.

30-32. (canceled)

33. A method according to claim 29 wherein converting PbOPbCO.sub.3 into alpha lead oxide comprises heating PbOPbCO.sub.3 in the presence of a flow of gas comprising an oxidiser at a temperature of at least 375 C.

34. (canceled)

35. A method of making a composition comprising Pb.sub.2O.sub.3, the method comprising: converting lead citrate into lead carbonate by heating the lead citrate in the presence of an oxidising gas and carbon dioxide, converting the lead carbonate into PbOPbCO.sub.3; and converting PbOPbCO.sub.3 into alpha lead oxide and converting alpha lead oxide into Pb.sub.2O.sub.3, by heating the PbOPbCO.sub.3 in the presence of a flow of gas comprising an oxidiser at a temperature of no more than 325 C.

36-41. (canceled)

42. A method according to claim 19, wherein the particles of lead citrate are rod-like and have a mean greatest dimension of at least 0.5 m, and no more than 20 m.

43-45. (canceled)

46. A composition producible, or produced by, the method of claim 19, comprising one or more of alpha lead oxide, beta lead oxide, metallic lead, Pb.sub.2O.sub.3 and Pb.sub.3O.sub.4, the composition comprising particles comprising sub-particles in the form of projections, the sub-particles having a mean greatest dimension of from 10 to 300 nm, and the composition having an acid absorption, determined using sulphuric acid, of at least 200 mg acid per g of sample.

47. A composition according to claim 46, wherein the composition comprises one or more of alpha beta oxide and beta lead oxide.

48. A composition according to claim 46, comprising metallic lead.

49. A composition according to claim 48, comprising at least 5 wt % metallic lead.

50. A composition according to claim 48 comprising no more than 40 wt % metallic lead.

51. A composition according to claim 46, wherein the composition comprises rod-like particles.

52. A composition according to claim 51 wherein the rod-like particles have a greatest dimension of from 0.2 m to 20 m.

53. A composition according to claim 51, wherein at least 50% by number of the particles of the composition are rod-like.

54. A composition according to claim 51, wherein, of the rod-like particles, at least 50% by number have a greatest dimension of from 0.2 m to 20 m.

55. A composition according to claim 51, wherein, of the rod-like particles, at least 50% by number have an aspect ratio of at least 1.5:1, and optionally have an aspect ratio of no more than 20:1.

56. A composition according to claim 46, wherein the sub-particles have a mean greatest dimension of at least 20 nm.

57. A composition according to claim 46, wherein the sub-particles have a mean greatest dimension of no more than 200 nm.

58. A composition according to claim 46, wherein the sub-particles have a mean greatest dimension of from 50 to 150 nm.

59. A composition according to claim 46, wherein at least 95 wt % of the composition comprises one or more of alpha lead oxide, beta lead oxide, metallic lead, Pb.sub.2O.sub.3 and red lead.

60. A composition according to claim 59, wherein at least 98 wt % of the composition comprises one or more of alpha lead oxide, beta lead oxide, metallic lead, Pb.sub.2O.sub.3 and red lead.

61. A composition according to claim 46, wherein the BET surface area of the composition as determined using nitrogen is at least 1.0 m.sup.2/g.

62. A composition according to claim 61, wherein the BET surface area of the composition is at least 2.5 m.sup.2/g.

63. A composition according to claim 46, comprising particles comprising a lead metal-rich and oxide-poor core portion, and an oxide-rich outer portion, the core portion optionally being spherical or sub-spherical.

64. A method of forming a lead-acid battery plate comprising combining the composition of claim 46 with one or more battery plate additives and an acid to form a paste.

65. A lead-acid battery plate producible, or produced, by the method of claim 64.

66. A lead-acid battery comprising one or more battery plates in accordance with claim 65.

Description

DESCRIPTION OF THE DRAWINGS

[0169] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0170] FIG. 1 shows a schematic representation of an example of a method of making alpha lead oxide in accordance with a first embodiment of the invention;

[0171] FIG. 2A shows a low-magnification scanning electron microscopy image of an example of a composition comprising alpha lead oxide in accordance with the second and tenth aspects of the invention;

[0172] FIG. 2B shows a high-magnification scanning electron microscopy image of an example of a composition comprising alpha lead oxide in accordance with the second and tenth aspects of the invention;

[0173] FIG. 3 shows a schematic representation of an example of a method of making a composition comprising beta lead oxide in accordance with a further embodiment of the invention;

[0174] FIG. 4A shows a low-magnification scanning electron microscopy image of an example of a composition comprising beta lead oxide in accordance with the fourth and tenth aspects of the invention;

[0175] FIG. 4B shows a high-magnification scanning electron microscopy image of an example of a composition comprising beta lead oxide in accordance with the fourth and tenth aspects of the invention;

[0176] FIG. 5 shows a schematic representation of an example of a method of making red lead in accordance with a further embodiment of the invention;

[0177] FIG. 6A shows a low-magnification scanning electron microscopy image of an example of a composition comprising red lead in accordance with the sixth and tenth aspects of the invention;

[0178] FIG. 6B shows a high-magnification scanning electron microscopy image of an example of a composition comprising red lead in accordance with the sixth and tenth aspects of the invention;

[0179] FIG. 7 shows a schematic representation of an example of a method of making Pb.sub.2O.sub.3 in accordance with a further embodiment of the invention;

[0180] FIG. 8A shows a low-magnification scanning electron microscopy image of an example of a composition comprising Pb.sub.2O.sub.3 in accordance with the eighth and tenth aspects of the invention;

[0181] FIG. 8B shows a high-magnification scanning electron microscopy image of an example of a composition comprising Pb.sub.2O.sub.3 in accordance with the eighth and tenth aspects of the invention;

[0182] FIG. 9 shows a schematic representation of an example of a method of making a composition comprising a desired component in accordance with a further embodiment of the invention;

[0183] FIG. 10 shows a schematic representation of an example of a method of making a battery plate in accordance with yet another embodiment of the invention;

[0184] FIG. 11 is a simplified perspective view of a battery in accordance with an embodiment of the invention;

[0185] FIGS. 12A and 12B show low-magnification scanning electron microscopy images of an example of a core of a particle derived from a composition comprising alpha lead oxide in accordance with the second and tenth aspects of the invention;

[0186] FIG. 13 shows the metal lead content in a powdered sample of a lead oxide in accordance with the present invention when it is exposed to air over time, compared to conventional lead oxides;

[0187] FIGS. 14A and 14B shows a low-magnification and a high-magnification scanning electron microscopy image, respectively, of an example of a particle of a composition comprising a lead oxide in accordance with the tenth aspect of the invention.

DETAILED DESCRIPTION

Methods of Forming Compositions Comprising Alpha Lead Oxide.

[0188] A composition comprising alpha lead oxide was synthesised as follows. 30 g of lead citrate (Pb.sub.3(C.sub.6H.sub.5O.sub.7).sub.2.Math.3H.sub.2O) was placed in a 4 litre rotary furnace. The lead citrate was made as disclosed in WO2008/056125. Scanning electron microscopy shows that the lead citrate is elongate, with particle lengths of about 10-40 m and particle widths of about 2-4 m. X-ray diffraction was used to confirm that the lead citrate was indeed lead citrate. A mixture of air (18 litres/hour) and carbon dioxide (18-25 litres/hour) was passed over the lead citrate while the lead citrate was heated up to 350 C., and then while the lead citrate was heated at 350 C. for a known, first period of between 1 hour 45 minutes and 2 hours. After this first period, a flow of nitrogen (12 litres/hour) was passed over the contents of the rotary furnace for a known, second period of from 3 to 30 minutes. The rotary furnace was then cooled to room temperature, with nitrogen being passed through the rotary furnace (12 litres/hour). The rotary furnace was rotated at a rate of 20 rpm throughout. The resulting composition was then analysed using x-ray diffraction and acid dissolution techniques to determine the presence, and relative amounts, of various components within the composition, such as alpha lead oxide, beta lead oxide, red lead and lead metal as described above in relation to the method of the first aspect of the present invention.

[0189] Table 1 below shows how the composition varies with process conditions. Dwell time 1 refers to the time that the lead citrate was heated and exposed to air and carbon dioxide. Dwell time 2 refers to the time that the contents of the rotary furnace were heated in the presence of nitrogen. In the Comparative Examples CEx1-CEx4, a mixture of air and carbon dioxide is passed through the rotary furnace at all times.

TABLE-US-00001 TABLE 1 formation of composition comprising alpha lead oxide CO.sub.2 Alpha flow Dwell Dwell Beta PbO PbO Pb.sub.3O.sub.2CO.sub.3 Pb metal rate time 1 time 2 Figures in parentheses - x-ray diffraction; Example VS no. (L/hour) (mins) (mins) figures not in parentheses - acid dissolution 1 168 80 115 5 (P) (D) (P) 2.5 (2) 2 170 80 105 15 (P) (D) (P) 3 (2) 3 178 14 120 30 72.07 (78) 20.33 (22) (0) 7.6 (0) 4 176 40 120 30 59.53 (61) 34.97 (37) (0) 5.5 (1) 5 172 80 120 30 21.32 (20) 75.58 (78) (0) 3.1 (2) 6 174 120 120 30 19.58 (17) 79.22 (81) (0) 2.2 (2) 7 184 160 120 30 0 (0) 99.30 (98) (0) 0.7 (2) 8 196 180 120 30 0 (0) 100 (99) (0) 0 (1) 9 186 200 120 30 0 (0) 97.80 (99) (0) 0 (1), +2 wt % C CEx 1 160 12 120 0 59.34 (69) 26.66 (31) (0) 13 (0), +1 wt % red lead CEx 2 164 19 120 0 (D) (P) (P) 4.6 (0) CEx 3 162 24 120 0 (P) (D) (P) 5.6 () CEx 4 166 80 120 0 (P) (P) (D) 0.7 (2)
Note that Pb.sub.3O.sub.2CO.sub.3 content was not measured using acid dissolution and carbon content was not measured using x-ray diffraction. In Table 1, P indicates present and D indicates dominant.

[0190] No carbon or red lead was found in any of the compositions of Examples 1-8. 2 wt % carbon was found in the composition of Example 9.

[0191] Examples 1 to 9 demonstrate that alpha lead oxide may be made by heating lead citrate in the presence of air and carbon dioxide, and then heating the reaction product in the presence of nitrogen.

[0192] Without wishing to be bound by theory, it is understood that the following reactions are taking place:

##STR00001##

[0193] Referring to FIG. 1, and without wishing to be bound by theory, it is anticipated that the method 100 of forming alpha lead oxide from lead citrate comprises converting 101 lead citrate into 2PbOPbCO.sub.3, and converting 102 2PbOPbCO.sub.3 into alpha lead oxide. It is anticipated that oxygen in the air reacts with the lead citrate to form a lead oxide (likely beta lead oxide) which then reacts with the carbon dioxide to form lead carbonate. Heating of the lead carbonate causes the formation of alpha lead oxide, which reacts with the lead carbonate to form 2PbOPbCO.sub.3. Heating of the 2PbOPbCO.sub.3 in an inert gas (in this case, nitrogen) causes the formation of alpha lead oxide.

[0194] It seems to be beneficial to provide an excess of carbon dioxide in order to promote the formation of the lead carbonate. It is also beneficial for the heating of the PbOPbCO.sub.3 in the inert gas to take place for a sufficiently long time to facilitate the formation of alpha lead oxide. It is anticipated that the use of the 250 litre/hour flow of carbon dioxide resulted in the formation of carbon due to the relatively low amounts of oxygen and relatively high amounts of carbon dioxide.

[0195] Examples 1-9 of Table 1 show that it is possible to produce a composition comprising a high percentage of alpha lead oxide. Furthermore, Examples 1-9 and Examples 3-9 in particular show that it is possible to control the relative amounts of alpha and beta lead oxide by controlling the relative amounts of air and carbon dioxide.

[0196] Scanning electron microscope images of the composition of Example 9 are shown in FIGS. 2A and 2B. The composition comprises larger, elongate particles 150, 151, 152 visible in FIG. 2A. Those particles have a similar shape and size to the particles of lead citrate used to make the alpha lead oxide. The particles have a mean length in excess of 5 m and a mean width of about 1-2 m. The surface of the particles appears to be roughened, with smaller sub-particles being visible on the surface of the particles. Small sub-particles 160, 161, 162 having a mean largest dimension of about 50-200 nm are visible.

Methods of Forming Compositions Comprising Beta Lead Oxide.

[0197] A composition comprising beta lead oxide was synthesised as follows. 30 g of lead citrate (Pb.sub.3(C.sub.6H.sub.5O.sub.7).sub.2.Math.3H.sub.2O) was placed in a 4 litre rotary furnace. The lead citrate was made as disclosed in WO2008/056125. Scanning electron microscopy shows that the lead citrate is elongate, with particle lengths of about 10-40 microns and particle widths of about 2-4 m. X-ray diffraction was used to confirm that the lead citrate was indeed lead citrate. A mixture of air (6-100 litres/hour) and nitrogen (12 litres/hour) was passed over the lead citrate while the lead citrate was heated up to 350 C., and then while the lead citrate was heated at 350 C. for 2 hours. The rotary furnace was then cooled to room temperature, with the same mixture of nitrogen and air being passed through the rotary furnace. The rotary furnace was rotated at a rate of 20 rpm throughout. The resulting composition was then analysed using x-ray diffraction and acid dissolution techniques to determine the presence, and relative amounts, of various components within the composition, such as alpha lead oxide, beta lead oxide, red lead and lead metal as described above.

[0198] Table 2 below shows how the composition varies with process conditions.

TABLE-US-00002 TABLE 2 formation of compositions comprising beta lead oxide Air Alpha Pb Red flow Beta PbO PbO metal lead Temp. rate Figures in parentheses - x-ray diffraction; Example VS no. ( C.) (L/hour) figures not in parentheses - acid dissolution 10 116(118) 350 100 60.43 (96) 1.26 (2) 33.55 (2) 3.5 11 118(120) 350 50 60.38 (91) 5.31 (8) 29.75 (1) 3.9 12 120(122) 350 30 69.75 (91) 6.13 (8) 19.75 (1) 3.6 13 136 350 24 77.43 (87) 10.68 (12) 8 (1) 3.0 14 130 350 18 77.70 (86) 12.65 (14) 5.95 (0) 3.7 15 132 350 12 82.81 (89) 9.31 (10) 3.25 (1) 3.7 16 134 350 6 91.70 (93) 6.90 (7) 0.6 (0) 0.8 17 138 300 24 91.19 (93) 6.86 (7) 0.15 (0) 1.8 18 140 400 24 81.26 (91) 8.04 (9) 10 (1) 0.7 19 144 350 24 82.24 (89) 10.16 (11) 5.6 (0) 2.0 20 148 350 24 79.98 (93) 5.16 (6) 8.1 (1) 5.9 21 150 350 15 82.53 (90) 9.17 (10) 3.4 (0) 4.9 22 154 350 15 79.30 (89) 8.02 (9) 9.8 (1) 1.1

[0199] In Example 19, there was no gas flow in the cooling stage i.e. after two hours of exposure to the mixture of air and nitrogen at 350 C. In Examples 20 and 21, nitrogen was omitted from the gas mixture, and as in Example 19 there was no gas flow in the cooling stage i.e. after two hours of exposure to air at 350 C. In Example 22, nitrogen was omitted from the gas mixture, but contrary to Examples 19-21 there was a 12 litres/hour flow of nitrogen in the cooling stage.

[0200] Examples 10 to 22 demonstrate that the controlled production of beta lead oxide may be achieved by heating lead citrate in a flow of air. Referring to FIG. 3, and without wishing to be bound by theory, it is anticipated that the method 200 of forming beta lead oxide from lead citrate comprises heating 201 lead citrate in the presence of an oxidising agent, in this case, oxygen in the air.

[0201] Examples 10 to 16 demonstrate that the use of high flow rates of air promotes the formation of beta lead oxide and lead metal, with some alpha lead oxide. As the amount of air decreases, the amount of beta lead oxide increases and the amount of lead metal decreases. Examples 10 to 16 demonstrate that it is possible to control the amount of lead metal in the composition by controlling the relative amounts of air and nitrogen.

[0202] Examples 13, 17 and 18 show that as the temperature at which the lead citrate is exposed to air and nitrogen is increased from 300 C. to 400 C., the amount of lead metal increases. Furthermore, scanning electron microscopy images show that the composition generated by heating to 300 C. comprises small sub-particles of about 50 m size, whereas the composition generated by heating to 400 C. comprises larger sub-particles of a few hundred microns size.

[0203] Without wishing to be bound by theory, the expected reaction mechanism is shown below:

##STR00002##

[0204] Scanning electron microscope images of the composition of Example 13 are shown in FIGS. 4A and 4B. The composition comprises larger, elongate particles 250, 251, 252 visible in FIG. 4A. Those particles have a similar shape and size to the particles of lead citrate used to make the alpha lead oxide. The particles have a mean length in excess of 5 m and a mean width of about 1-2 m. The surface of the particles appears to be roughened, with smaller sub-particles being visible on the surface of the particles. Small sub-particles 260, 261, 262 having a mean largest dimension of about 50-200 nm are visible.

Methods of Forming Compositions Comprising Red Lead.

[0205] A composition comprising red lead was synthesised as follows. 30 g of lead citrate (Pb.sub.3(C.sub.6H.sub.5O.sub.7).sub.2.Math.3H.sub.2O) was placed in a 4 litre rotary furnace. The lead citrate was made as disclosed in WO2008/056125. Scanning electron microscopy shows that the lead citrate is elongate, with particle lengths of about 10-40 m and particle widths of about 2-4 m. X-ray diffraction was used to confirm that the lead citrate was indeed lead citrate. A mixture of air (18 litres/hour) and carbon dioxide (200 litres/hour) was passed over the lead citrate while the lead citrate was heated to 350 C., and then while the lead citrate was heated at 350 C. for two hours. After this first period, a flow of air (200 litres/hour) was passed over the contents of the rotary furnace for a known, second period of 30 or 60 minutes. The rotary furnace was then cooled to room temperature, with air being passed through the rotary furnace (200 litres/hour). The rotary furnace was rotated at a rate of 20 rpm throughout. The resulting composition was then analysed using x-ray diffraction and acid dissolution techniques to determine the presence, and relative amounts, of various components within the composition, such as alpha lead oxide, beta lead oxide, red lead and lead metal as described above.

[0206] Table 3 below shows how the composition varies with process conditions. Dwell time 2 is the duration of heating in the flow of air. Dwell temp. is the temperature at which the product is heated in the flow of air.

TABLE-US-00003 TABLE 3 formation of compositions comprising red lead Alpha Red Pb Dwell Dwell Beta PbO PbO Pb.sub.2O.sub.3 lead metal time 2 temp Figures in parentheses - x-ray diffraction; Example VS no. (mins) ( C.) figures not in parentheses - acid dissolution 23 180 30 350 0 (0) 61.60 (62) 37.8 (38) 0 (0) 0.65 (0) 24 188 60 350 0 (0) 48.00 (48) 35 (35) 16 (16) 0.00 (1) 25 190 60 370 0 (0) 30.60 (30) 0 (0) 69.4 (68) 0 (2) 26 192 60 390 0 (0) 24.00 (24) 0 (0) 76 (76) 0 (0) 27 194 60 410 0 (0) 0 (0) 0 (0) 100 (100) 0 (0)

[0207] Examples 23 to 27 demonstrate that it is possible to make red lead and compositions with a high percentage of red lead by heating lead citrate in a flow of air and carbon dioxide, and then heating the reaction product in a flow of air. The use of higher temperatures during the heating in air promote the formation of red lead. Referring to FIG. 5, and without wishing to be bound by theory, it is anticipated that the method 300 of forming red lead from lead citrate comprises converting 301 lead citrate into PbOPbCO.sub.3, and converting 302 PbOPbCO.sub.3 into red lead.

[0208] Without wishing to be bound by theory, it is believed that the following reactions are occurring.

##STR00003##

[0209] Converting 301 lead citrate into PbOPbCO.sub.3 comprises heating the lead citrate to form beta lead oxide, which reacts with carbon dioxide to form lead carbonate. The lead carbonate decomposes on heating to form alpha lead oxide, which reacts with lead carbonate to form PbOPbCO.sub.3. Heating of the PbOPbCO.sub.3 in a stream of air causes the formation of alpha lead oxide, which reacts with oxygen to form red lead.

[0210] Scanning electron microscope images of the composition of Example 27 are shown in FIGS. 6A and 6B. The composition comprises larger, elongate particles 350, 351, 352 visible in FIG. 6A. Those particles have a similar shape and size to the particles of lead citrate used to make the alpha lead oxide. The particles have a mean length in excess of 5 m and a mean width of about 1-2 m. The surface of the particles appears to be roughened, with smaller sub-particles being visible on the surface of the particles. Small sub-particles 360, 361, 362 having a mean largest dimension of about 50-100 nm are visible.

Methods of Forming Compositions Comprising Pb.sub.2O.sub.3

[0211] A composition comprising Pb.sub.2O.sub.3 was synthesised as follows. 30 g of lead citrate (Pb.sub.3(C.sub.6H.sub.5O.sub.7).sub.2.Math.3H.sub.2O) was placed in a 4 litre rotary furnace. The lead citrate was made as disclosed in WO2008/056125. Scanning electron microscopy shows that the lead citrate is elongate, with particle lengths of about 10-40 m and particle widths of about 2-4 m. X-ray diffraction was used to confirm that the lead citrate was indeed lead citrate. A mixture of air (18 litres/hour) and carbon dioxide (200 litres/hour) was passed over the lead citrate while the lead citrate was heated up to 350 C., and then while the lead citrate was heated at 350 C. for two hours. After this first period, a flow of air (between 30 and 200 litres/hour) was passed over the contents of the rotary furnace for a known, second period of 30 to 120 minutes at a temperature of 300 C. or 350 C. The rotary furnace was then cooled to room temperature, with air being passed through the rotary furnace (200 litres/hour). The rotary furnace was rotated at a rate of 20 rpm throughout. The resulting composition was then analysed using x-ray diffraction and acid dissolution techniques to determine the presence, and relative amounts, of various components within the composition, such as alpha lead oxide, beta lead oxide, red lead and lead metal as explained above.

[0212] Table 4 shows how the composition varies with processing conditions.

TABLE-US-00004 TABLE 4 formation of compositions comprising Pb.sub.2O.sub.3 Air Metal flow Dwell lead Alpha PbO Pb.sub.2O.sub.3 Red Lead rate Temp. time 2 Figures in parentheses - x-ray diffraction; Example (L/hour) ( C.) (mins) figures not in parentheses - acid dissolution 28 200 350 30 68 (68) 32 (32) 29 200 350 60 (1) 48.5 (48) 35.4 (35) 16.2 (16) 30 100 350 30 40 (40) 60 (60) 31 30 350 30 (1) 46.46 (46) 53.53 (53) 32 100 350 60 25 (25) 29 (29) 46 (46) 33 100 330 60 41 (41) 59 (59) 34 100 330 120 33 (33) 52 (52) 15 (15) 35 100 300 120 (1) 36 (36) 63.63 (63) 36 100 300 240 31 (31) 69 (69)

[0213] The temperature referred to in Table 4 is the temperature at which the contents of the rotary furnace are exposed to air. The duration referred to in Table 4 is the duration for which the contents of the rotary furnace are exposed to air.

[0214] Examples 28 to 36 demonstrate that it is possible to make compositions with a high percentage of Pb.sub.2O.sub.3 by heating lead citrate in a flow of air and carbon dioxide, and then heating the reaction product in a flow of air, preferably at a relatively low temperature (in this case, 300 C. seems to be preferred). The use of higher temperatures during the heating in air promotes the formation of red lead, whereas the use of lower temperatures during the heating in air promotes the formation of Pb.sub.2O.sub.3.

[0215] Referring to FIG. 7, and without wishing to be bound by theory, it is anticipated that the method 400 of forming red lead from lead citrate comprises converting 401 lead citrate into PbOPbCO.sub.3, and converting 402 PbOPbCO.sub.3 into Pb.sub.2O.sub.3. Converting 401 lead citrate into PbOPbCO.sub.3 comprises heating the lead citrate to form beta lead oxide, which reacts with carbon dioxide to form lead carbonate. The lead carbonate decomposes on heating to form alpha lead oxide, which reacts with lead carbonate to form PbOPbCO.sub.3. Heating of the PbOPbCO.sub.3 in a stream of air causes the formation of alpha lead oxide, which reacts with oxygen to form Pb.sub.2O.sub.3.

[0216] Without wishing to be bound by theory, it is believed that the following reactions are occurring.

##STR00004##

[0217] Scanning electron microscope images of the composition of Example 36 are shown in FIGS. 8A and 8B. The composition comprises larger, elongate particles 450, 451, 452 visible in FIG. 6A. Those particles have a similar shape and size to the particles of lead citrate used to make the alpha lead oxide. The particles have a mean length in excess of 5 m and a mean width of about 1-2 m. The surface of the particles appears to be roughened, with smaller sub-particles being visible on the surface of the particles. Small sub-particles 460, 461, 462 having a mean largest dimension of about 50-100 nm are visible.

[0218] Compositions comprising alpha lead oxide, beta lead oxide, red lead and Pb.sub.2O.sub.3 in accordance with the present invention were investigated to determine their BET surface area, pore volume and pore diameter. These were determined using sample sizes of about 0.55-0.60 g, a bath temperature of 77 K and N.sub.2 as the analytical adsorptive.

TABLE-US-00005 TABLE 5 some characteristics of compositions in accordance with the present invention Pore diameter BET surface Pore volume () (based on Sample area (m.sup.2g.sup.1) (cm.sup.3g.sup.1) adsorption) Alpha lead 2.17 0.00734 274 oxide Beta lead oxide 2.67 0.0127 267 Red lead 2.58 0.0109 299 Pb.sub.2O.sub.3 3.31 0.0139 240

[0219] The structure of beta lead oxide in accordance with the fourth, tenth and eleventh aspects of the present invention was investigated. Sticky carbon tape was covered relatively evenly with beta lead oxide in accordance with the present invention and conventional ball mill lead oxide. The powdered lead oxides were then pressed to embed the powders firmly into the tape. 1 drop of 1 wt % acetic acid solution was added to slowly dissolve the PbO. After 30 sec., excess solution was removed with dry paper. This process of wetting with acetic acid and removing excess solution was repeated four times. The remaining material was then rinsed four times with a drop of distilled water.

[0220] FIGS. 12A and 12B show the particles that remain after the particles were exposed to acetic acid. The remaining particles are essentially spherical or sub-spherical (essentially, resembling a sphere), and are about 15-30 m in diameter. Each of the remaining particles is essentially a core of the original particle. Given that a 1 wt % acetic acid solution would only dissolve PbO and not Pb, the core is essentially made of lead metal. The outer region comprising lead oxide has been dissolved by the acetic acid. This provides evidence of a lead oxide structure comprising a lead metal core covered by an outer region of lead oxide. Such a structure is beneficial because the lead oxide protects the inner lead metal from oxidation in the event that the composition is exposed to a potentially-oxidising environment (such as the air).

[0221] One of the main properties measured by battery manufacturers to determine the performances of a lead oxide is acid absorption. The acid absorption characteristics of the materials described above in relation to FIGS. 12A and 12B were investigated, and compared to conventional ball mill and Barton pot lead oxides. A 22 g (20 ml) solution of 16 wt % sulfuric acid was prepared and cooled to room temperature. 10 g of lead oxide was then added under stirring at 350 rpm in an insulated vessel. The suspension was left to react for 20 min before analysis. H.sub.2SO.sub.4 absorption was determined by titration of unreacted H.sub.2SO.sub.4 with NaOH, it was also correlated with temperature rise in the suspension during reaction. The mass percentage of lead oxide reacted was also determined.

TABLE-US-00006 TABLE 6 acid absorption characteristics of alpha and beta leady oxides of the present invention Beta lead Alpha lead oxide of the oxide of the present present Barton Pot Ball Mill invention invention Acid 150.8 184.9 232.6 258.9 absorption (mg H.sub.2SO.sub.4/g sample) Temperature 11.35 12.5 17.1 17.7 increase ( C.) Mass 34% 42% 52.9% 58.9% percentage of leady oxide reacted (wt %)

[0222] The data of Table 6 show that the acid absorption characteristics of the alpha and beta lead oxides of the present invention are superior to conventional Barton pot and ball mill lead oxides. Furthermore, the mass percentage of the lead oxide reacted is far greater for the alpha and beta lead oxides of the present invention than for the conventional lead oxides.

[0223] The surface area and pore volume were measured for the materials studied in Table 6, and are shown in Table 7.

TABLE-US-00007 TABLE 7 surface area and pore volume for alpha and beta leady oxides of the present invention Barton pot Ball mill Beta PbO Alpha PbO Surface area 0.44 1.34 1.08 1.96 BET (m.sup.2 .Math. g.sup.1) Pore volume 0.00175 0.004478 0.00620 0.011 (cm.sup.3 .Math. g.sup.1)

[0224] The stability of the metallic lead in the materials described above in relation to FIGS. 12A and 12B were investigated. The metallic lead content of the lead oxide in accordance with the present invention (x) was compared to known Barton pot (o) and ball mill (+) lead oxides. Metallic lead content was determined by reaction with an acid or alkali. FIG. 13 shows how the metallic lead content varies with time. It is clear from FIG. 13 that there is a far lower rate of loss of metallic lead for the lead oxide of the present invention than for the conventional lead oxides.

[0225] Scanning electron microscope images of an example of a composition in accordance with the tenth aspect of the present invention are shown in FIGS. 14A and 14B. FIG. 14A is a low magnification image, which shows an agglomerated particle AG, which has a network of channels and pores therein. The particle AG has an ill-defined amorphous shape. As shown in FIG. 14B, the particles comprise multiple sub-particles, two of which are labelled SP1 and SP2. The sub-particles have a mean greatest dimension of about 50-100 nm.

[0226] An example of a method in accordance with an embodiment of the ninth aspect of the present invention will be described with reference to FIG. 9. The method is denoted generally by reference numeral 500, and is a method of producing a composition comprising a desired one or more of alpha lead oxide, beta lead oxide, Pb.sub.2O.sub.3, red lead and lead metal. The method 500 comprises determining 501 which of alpha lead oxide, beta lead oxide, Pb.sub.2O.sub.3, red lead and lead metal is or are desired in the composition. In this particular example, we determine 501 that a composition comprising red lead is desired. The method 500 comprises, based on said determination, selecting 502 one or more reaction parameters from the list consisting of one or more heating temperatures, one or more heating durations and one or more gas compositions. As has been demonstrated above, in order to make a composition comprising red lead, we heat lead citrate in a mixture of air and carbon dioxide, and then heat the resulting composition in a stream of air at a temperature of 400 C. In this connection, we therefore select 502 a first gas composition comprising carbon dioxide and air in which the lead citrate will be heated. We also select a second gas composition comprising air for subsequent heating at 400 C., the second gas composition comprising air. We then heat the lead citrate at 350 C. for two hours in a mixture of air and carbon dioxide, and then heat the resulting composition in air for an hour at 400 C., thereby forming a composition comprising red lead.

[0227] An example of a method of making a battery plate in accordance with yet another embodiment of the invention will now be described with reference to FIG. 10. The method of forming lead acid battery plates is denoted generally by reference numeral 600. The method 600 comprises combining 601 a composition of the second, fourth, sixth and/or eighth aspects of the present invention with one or more battery plate additives and an acid to form a paste. Sulfuric acid will typically be used as the acid, which converts the lead oxide in the composition into PbSO.sub.4. Suitable battery plate additives include those listed above and include metal compounds, insoluble carbon, barium sulphate and fibres, such as lignin-based fibres. The paste may then be applied 602 to a grid, typically a lead-alloy grid, and allowed to cure 603 to form a lead acid battery plate.

[0228] FIG. 11 is a simplified exploded perspective view of a battery in accordance with an embodiment of the invention. The battery is denoted generally by reference numeral 1000 and comprises a plurality of battery plates only one of which 1001 is labelled. The battery plate 1001 is a battery plate made as describe above in relation to the method of FIG. 10. The battery plates 1001 are located in a plastics casing 1003. Sulphuric acid is provided in the casing 1003 and is in contact with the battery plates 1001.

[0229] Many of the methods mentioned above comprise an oxidation process, which is sometimes followed by a thermal decomposition process, depending on the method. The oxidation processes are generally exothermic, while the thermal decomposition processes are generally endothermic. The net energy required is the difference between heat absorbed in the endothermic process and the heat produced by the exothermic process, thus the energy required for the process may be relatively low, may be neutral but sometimes, net energy is available from the process.

[0230] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0231] In some of the examples above nitrogen is used as an inert gas. Those skilled in the art will realise that other inert gases may be used, such as any of the noble gases.

[0232] The examples above show how air is used to provide molecular oxygen as an oxidising agent. Those skilled in the art will realise that oxidising agents other than molecular oxygen may be used. Furthermore, the molecular oxygen need not be provided in air.

[0233] The inventors have demonstrated that the compositions in accordance with the present invention have been made using the methods described herein. Those skilled in the art will realise that other methods may be used to arrive at the composition in accordance with the present invention.

[0234] The examples above demonstrate the use of lead citrate as a starting material. Those skilled in the art will realise that other organic lead salts may be used. In particular, those skilled in the art will realise that other lead carboxylates may be used.

[0235] The examples above use lead citrate having a particulate size and shape. Those skilled in the art will realise that lead citrate having a different shape and size may be used.

[0236] The methods exemplified above use a rotary furnace. Those skilled in the art will realise that other furnaces or reaction vessels may be used.

[0237] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.