US3094445A - Method of generating heat and light - Google Patents

Description

United YStates arent METHD (lll GENERATING HEAT AND LlGli'i Robert S. Bush, Midland, Donald L. Lernen, Freeland,

and Martin A. Molnar, Sanford, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Sept. 2S, 1959, Ser. No. 845,589

6 Claims. (ill. 149--37 The invention relates to a method of generating heat and light and more particularly relates to an improved ,method of generating heat and light by the combustion of magnesium or magnesium-base'alloy.

This is a continuation-impart of the copending application Serial No. 700,905, led December 5, 1957, now abandoned.

For the purposes of the specification and claims, magnesium and magnesium-base alloy containing at least 75 percent by weight of magnesium are hereinafter referred to as magnesium metal.

'Heretofore in generating heat and light by burning a magnesium metal the problem has arisen that When a bulky piece of magnesium metal is burned as by igniting an edge or end of it a substantial proportion of the metal melts ahead of the flame or 1ourning area and drips oil'. In some applications in which a magnesium metal is burned to produce light as in dares or to produce heat as in devices utilizing magnesium metal as a solid fuel, it is important to prevent this dripping of molten metal and thus to permit substantially all of the magnesium to burn in place in the device.

It is accordingly an object of the invention to provide a method of generating heat and light by the combustion of magnesium metal in such a manner that the magnesium metal burns without dripping.

lIt is another object of the invention to provide a method of generating heat and light using magnesium metal fuel in such a manner that the fuel is efficiently and smoothly consumed upon ignition.

A still further object of this invention is to generate heat and light in a manner which permits the use of magnesium metal in a form having substantially the maximum amount of magnesium attainable per unit volume.

The present invention is based upon the discovery that by admixing a suitable proportion of a solid nonmetallic substance having a relatively high melting point or decomposition temperature (that is above 450 F.) with a suitable particulate solid form of magnesium metal and die expressing the mixture at a temperature at which the metal particles undergo a welding together during the die expression but below a temperature at which the occluded nonmetallic solid melts or decomposes a product is obtained which upon being ignited produces heat and light as it burns, the burning is steady, and the burning product remains substantially coherent and does not drip molten magnesium metal.

The action of the admixed nonmetallic substance is not entirely understood but it is believed that it serves both as an insulator and diluent. As an insulator, it retards the transfer of heat away from the burning surface so that tlame propagation continues steadily from the point of ignition without leaving unburncd sections. AS a diluent it moderates the burning rate so that burning takes place more smoothly with less sputtering and heat and light are generated in a more uniform manner, the brightness of the light being substantially that of ordinary magnesium.

ln contrast upon igniting an article formed of a magnesium metal which contains substantially no nonmetallic substance the article burns in a manner which is entirely different and quite undesired for the production of heat and light. In this case the heat of combustion is conducted ahead of the flame so efficiently that metal in the combustion zone melts too rapidly to be consumed and drips from the unmelted mass. It is also believed that as another consequence of the eflicient heat transfer away from the combustion site ignition tends to occur at isolated points ahead of the main flame propagation. As a result, the metal between multiple sites where combustion is occurring becomes molten and drips or sputters from the article sometimes carrying the burning portions from the main mass so that the generation of heat and light stops.

While a nonmetallic substance which does not form a fluid except at an elevated temperature is generally applicable in pulverulent form for coextrusion to form the product used in accordance with the invention, an effective product is formed using magnesium oxide, calcium oxide or strontium oxide. A fluid is meant to include a liquid generated as by melting and a gas generated as by decomposition.

When even more effective moderation of combustion of the product used in this invention is desired, the article is advantageously made using a carbonate lof one of the second group metals cadmium or magnesium as the nonmetallic substance. Various carbonates of the aforesaid second group metals muy be used in pulverulent form, for example magnesite (MgCOg), nesquehonite hydromagnesite (3l\flgCO3Mg(Ol-l)23H2O), lansfordite (MgCOg-Sl-lg), artinite (MgCO3-Mg(OH)2-3H2O), cadmium carbonate (CdCOg). Af these, the heavy basic carbonate, hydromagnesite, is preferred. These materials are normally in a finely divided state, for example in particles smaller than about 50 microns. A preferred range of particle size is from 0.1 to 5 microns.

Upon admixing such a carbonate with particulated magnesium metal and die expressing the mixture at a temperature at which the metal particles undergo a welding together but below a temperature at which the sooccluded carbonate decomposes an article is obtained which upon being ignited expands ahead of the llame, burns steadily, does not drip molten magnesium metal and generates heat and light in a uniform manner until it is consumed. The expansion in the hot zone ahead of the flame occurs as the occluded carbonate decomposes so as to produce gas under pressure in the interstices of the particulate die expressed metal, the die expressed article swells and its structure becomes cellular. rthe cellular material so-obtained during combustion serves effectively to insulate the remainder of the article being burned so that flame propagation continues smoothly from the point of the ignition.

The invention then consists of the aforesaid method of generating heat and light which consists of forming and igniting a magnesium metal product which does not drip on burning, `the method being herein fully described and particularly pointed out inthe claims.

ln the process of making the article employed in the method of the invention, the magnesium metal to be coextruded is suitably comminuted as by grinding, filing, shaving, atomizing or other appropriate method. The particular shape of the metal particles does not appear to be critical.

The particulated metal and the pulverulent nonmetallic solid are mixed together in suitable proportions whereby to at least partially coat the metal particles with nonmetallic particles which are preferably dust like and more or less adhere to the metal particles. The amount of nonmetallic substance to use may range from about 0.5 to 20 percent of the weight of the metal, the preferred amount being about 5 percent in the case of a carbonate of magnesium or l5 percent in the case of cadmium carbonate. Generally satisfactory results are had with from about 2 to 8 percent of magnesium carbonate, for example. Mixing can be eifected in various ways as for example by tumbling the metal and nonmetal particles together in a closed vessel, such as a barrel which is turned end over end. Mixing in which the particles are tumbled about in a vessel revolving a 50 r.p.m. can be accomplished satisfactorily in 3 to 4 minutes, but other mixing times may be used.

The mixture iof metal and nonmetallic particles is charged into the container of an extrusion press and die expressed at 4a temperature somewhat lower, for example 25 to 350 Fahrenheit degrees lower, than that which would be suitable for the extrusion of the metal alone as understood in the metal extrusion art. In the case of magnesium-base alloys, for example, the ltemperature of the charge in the container may be 'as low as 300 F. It is desirable to avoid extrusion temperatures at which excessive decomposition or melting of the nonmetallic material occurs Yand for this 4reason it is preferable to extrude the charge at as low a temperature as practicable without incurring the use of excessive pressures which tend to produce excessive wear on the extrusion dies and other parts of the extrusion apparatus. Satisfactory extrusion results can be obtained lover a wide range of temperatures, as for example 300 to 850 F., 450 to 650 being generally suitable. The extrusion or die expressing operation welds the metal particles to' gether into a rigid body consisting of a matrix of metal in which the nonmetallic particles are dispersed as more or less discrete masses enveloped in the metal.

Reduction during extrusion is preferably 4 to 1. The extruded shape may be in any desired form obtainable from the die such as `a rod, bar ribbon, or tube.

In carrying out the method oi' the invention, the extruded metal product may be mounted, if desired, in a suitable device, such as a are or other holder. The product is ignited by means of a flame, fuse or thermit initiator or other suitable heat producing initiator.

Example l More or less spherical particles of ZK60, a magnesiumbase alloy having a nominal composition of 6 percent zinc, 0.6 percent zirconium, the balance magnesium, were mixed with percent by weight of magnesium oxide. Mixing was accomplished by tumbling the metal and oxide particles in a cylindrical one gallon container on a ball mill stand for 3 to 4 minutes. The resulting mixture was placed in a horizontal ram extrusion press `and extruded through a 1 inch `diameter die opening at a container temperature of 500 F. and a die temperature of 500 F. A 1 inch diameter rod was extruded at a speed of approximately 0.5 foot per minute.

A section of this extrude was mountedl at one end in a clamp and the other end ignited by means of a welding torch. The burning thereby initiated proceeded steadily to produce heat and light in a uniform manner without dripping molten metal.

Example Il Particles of magnesium-base alloy ZK60 in the form of lings and sawdust were mixed with 5 percent by weight of hydromagnesite. Mixing was accomplished by tumbling the metal and carbonate particles in a cylindrical one gallon container on a ball mill stand for 10 to l5 minutes. The resulting mixture was charged into the container of a horizontal ram extrusion press iitted with a die having a yone inch diameter opening and extruded in the manner described in Example I.

A section Aof the resulting extrude was mounted at one end iny a clamp. The other end was ignited by means of a welding torch. The so-ignited extrude expanded ahead of the llame. Burning of the extrude proceeded steadily to produce heat and light in a uniform manner without dripping molten metal.

Example III More 'or less spherical particles of ZK60 magnesiumbase alloy were mixed with 15 percent by Weight of cadmiurn carbonate. Mixing was `accomplished by tumbling the metal Iand carbonate particles in a cylindrical one gallon container on a ball mill stand for 10 to l5 minutes. The resulting mixture was charged into the container of a horizontal ram extrusion press fitted with a die having a one inch diameter opening and extruded in the manner described in Example I. A section of the resulting extrude was mounted at one end in ya clamp. The other end was ignited by means of a welding torch and found to expand ahead of the llame. The burning proceeded steadily to produce heat and light in a uniform manner Without dripping molten' metal.

By way of a comparison more or less spherical particles of ZK60 magnesium-base alloy were placed in a horizontal ram extrusion press and extruded through a one inch diameter die Opening at a container temperature of 550 F. and a die temperature of y600 F. A one inch diameter rod was extruded at a speed of approximately 0.5 foot per minute.

A section of the resulting extrude was mounted at one end in a clamp. The other end was ignited by means of a welding torch. The so-ignited extrude produced heat and light in an entirely sporadic manner. As burning progressed the extrude ignited at many points on its surface and unburned molten metal dripped from the burning extrude.

By way of an additional comparison a portion of more or less spherical particles of ZK60 magnesium-base alloy was mixed with 5 percent by weight of hydromagnesite based on the weight of the metal particles. Mixing was accomplished by tumbling the metal and hydromagnesite particles together in a cylindrical one gallon container on a ball mill stand for about an hour. A 1250 gram charge of the resulting mixture was placed in a horizontal ram extrusion press having a 4 inch diameter container. The die opening of the press was blocked olf. The container and die were maintained at a temperature `of about 550 F. while the said charge was compressed and held under a compacting pressure of 475 tons for 2 minutes. The die was then removed from the press and the compact was ejected. After it had been allowed to cool the ejected compact was machined into the form of a rectangular bar 0.5 inch x 0.5 inch x 3 inches. The bar was cantilever supported by means of a clamp in a laboratory hood land ignited at the free end with an acetylene torch. Almost instantaneously the ignited end of the bar exploded showering burning magnesium metal particles over an area 5 feet in radius and extinguishing or removing all burning metal from the bar. The end of the remaining portion of the bar was again ignited and again the ignited end immediately exploded, scattering burning magnesium metal particles and extinguishing all burning of the remaining part of the bar held by the clamp.

What is claime-d is:

l. In the heat and light generating combustion of a magnesium metal, the improvement which consists` in employing as the combustible material, `a rigid solid consisting essentially of a physical admixture consisting of 0.5 to 2O percent by weight of a particulated substance, the balance particulated magnesium metal thereby to avoid dripping molten metal during combustion, said rigid solid being in the -form of an extrude, and said particulated substance being selected from the group consisting of the oxides, carbonates and basic carbonates of magnesium, calcium, strontium, cadmium.

2. In the heat and light generating combustion of a magnesium metal, the improvement which consists in employing as the combustible material a rigid solid consisting essentially of an intimate admixture consisting of 0.5 to 20 percent by weight of a particulated substance selected from the group consisting of oxides, -carbonates and basic carbonates of magnesium, cadmium and the alkaline earth metals, the balance particulated magnesium metal, said combustible material having the form of an extrude prepared by die expressing said admixture at a temperature in the range of 300 to 850 F. whereby the magnesium metal particles undergo a welding together during die eX- pression, but below the temperature at which the substance forms a uid, thereby to aviod dripping molten metal during combustion.

3. The method as in claim 1 in which the particulated substance is a basic carbonate of one of the said magnesium, calcium, strontium, cadmium.

4. The method as in claim 1 in which the particulated substance is `a carbonate of one of the said magnesium, calcium, strontium, cadmium.

5. The method as in claim 4 in which the carbonate is hydromagnesite.

6. The method as in claim 1 in which the substance is an oxide of one of the said magnesium, calcium, strontium, cadmium.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Goetzel: Treatise on Powder Metallurgy, volume I, 1949, p. 196.

Frazier: Proceedings 14th Annual Meeting, Metal Powder Association, April 21-3, 1958, p. 69.

Claims (1)

1. 2. IN THE HEAT AND LIGHT GENERATING COMBUSTION OF A MAGNESIUM METAL, THE IMPROVEMENT WHICH CONSISTS IN EMPOLYING AS THE COMBUSTIBLE MATERIAL A RIGID SOLID CONSISTING ESSENTIALLY OF AN INTIMATE ADMIXTURE CONSISTING OF 0.5 TO 20 PERCENT BY WEIGHT OF A PARTICULATED SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF OXIDES, CARBONATES AND BASIC CARBONATES OF MAGNESIUM, CADMINUM AND THE ALKALINE EARTH METALS, THE BALANCE PARTICULATED MAGNESIUM METAL, SAID COMBUSTIBLE MATERIAL HAVING THE FORM OF AN EXTRUD PREPARED BY DIE EXPRESSING SAID ADMIXTURE AT A TEMPERATURE IN THE RANGE OF 300 TO 850*F. WHEREBY THE MAGNESIUM METAL PARTICLES UNDEGO A WELDING TOGETHER DURING DIE EXPRESSION, BUT BELOW THE TEMPERATURE AT WHICH THE SUB STANCE FROM A FLUID, THEREBY TO AVOID DRIPPING MOLTEN METAL DURING COMBUSTION.