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Crystals of high-temperature materials produced in the solar furnace
Crystals of High-Temperature Materials Produced in the Solar Furnace E r i c h A. Farbcr Professor q nd Resettrch Professor, Mechanical Engineering, University of Florida
REAT emphasis is put on space exploration today and experts believe t h a t one of the first tools available on the moon will be a solar furnace. One phase of our solar energy work has been to investigate ways in which a solar furnace could be used by a lunar station in support of its objectives. Things which can be done on the moon or extracted from lunar materials could eliminate transportation from the earth to the moon, an expensive, and timeconsuming process. T o d a y ' s best available sources regarding the most abundant materials to be found on the moon give O2 and H2 in compound form, Si, Fe, Mg, A1, Ca, etc. On the basis of this information the following objectives have been formulated: A - - T o extract water from simulated lunar materials, then to dissociate this water into hydrogen and oxygen, which can be stored as fuel and used at a later date by recombination. B - - T o grow crystals from simulated lunar materials and by a study of these crystals and their properties to obtain a better understanding of the fundamental nature of matter.
G
Manuscript received June 10, 1963.
FIG. 1--Solar furnace in operation 38
C - - L a t e r , if desirable, to take some of these crystals and by doping them change their characteristics as to produce "solar cells" for direct conversion of solar energy into electricity or optical masers for communication. This paper discusses the first part of objective B, the growing of crystals. A number of the crystals grown in the solar furnace at the University of Florida Solar Energy Laboratory, Fig. 1, are believed to be the first ones of their kind.
FIG. 2--Targets : can (left) ; pellet (right).
FIG. 3--Target irradiated in furnace ! No.a~ Energg
To produce these crystals, targets were prepared from materials in powder form (believed to be the state of matter on the surface of the moon). The powders were either put into cans with plastic or crystal glass covers to keep the powders from falling out, or pressed and sometimes sintered into pellets, eliminating the container all together. Fig. 2. When these targets are irradiated in the solar furnace, Fig. 3, the powder melts and fuses, forming a liquid puddle within which, upon cooling, crystals are found. A crater develops and becomes deeper the longer the sample is irradiated. In some cases the crater was repacked with powder periodically to increase the size of the melt, which, in turn, had a direct bearing on the size of the crystals produced. Crystals l~ cm in length and about 0.5 cm thick have been grown in this man-
FIG.
ner. Some difficulty was experienced in getting the crystals out of the melt in one piece. Another method used successfully was vapor deposition. A crater was burned into the target in the above manner. Then only one side of the crater was heated with the vapors produced made to stream over the cool edge of the crater on the other side. By this method vapors condensed and formed perfect crystals. These vapor-deposited crystals were smaller than tlle ones produced in the melt. hnpure materials could be used, inasmuch as during the heating, impurities vaporize or diffuse into the cooler regions or zones leaving pm'e and clear crystals. AfteR' removing the sample from the irradiating beam it cools, Fig. 4, and the crystals are formed and grown. Fig. 5 shows the cold crater with snmll crystals (about 2 mm on the side), looking like teeth in a mouth, near the center of the crater. Under longeR' irradiation a smooth bottom crater is formed, Fig. 6, and if repacked periodically a largeR' and thicker melt is produced. The outer regions of the target around a typical crater are not affected by the heat, thus, are still in powder form. Nearer the crater the powder is sintered due to the exposure to heat. Still closer to the crater small but perfect crystals are found, Fig. 7, formed by vapor deposition as explained above. These crystals become more numerous as the edge of the crater is approached and combine into some typical formations such as the "christmas trees" shown in Fig. 8. Names like these have been given to the most frequently observed formations to simplify discussion of them. The crater bottom itself is a smooth, thick, glassy
4--T~rget cooling
FIG. 5--Irradiated target, small crystals near center Vol. 8, No. 1, 19b'~
FI~. 6--Irradiated target, deep crater 39
FIG. 9
Crater b o t t o m
FIG. 7--CaO crystals, vapor deposition
FIG. 10--Large crystal inbedded in melt FIG. 8--CaO crystal formations near crater edge mass, Fig. 9, with cleavage lines visible between the individual crystals which formed during the cooling process. A large imbedded crystal is seen in Fig. 10. Often these crystals broke into smaller ones, splitting along their crystal faces, as they were pried from the melt. 40
When the melt is broken in half, the cross-section, Fig. 11, shows the crystals imbedded and with some of their faces exposed. The thicker the melt, a function of repacking repeatedly and irradiating for longer periods, the larger are the crystals produced. Larger CaO crystal pieces produced in the melt are shown in Figs. 12 and 13. They are about 5 mm in size. At the beginning of this work the minimum useful Solar Energy
FIG. ll--Crater bottom cleavage, inbedded CaO crystals
FIG. 13--CAO crystal twins, perfect optical quality, (5 mm)
FIG. 12--CAO crystal fragment, perfect optical quality, (3 mln) crystal size was set at 1 m m on a side. This seemed to be the minimum crystal size necessary for the deterinination of the physical properties. Actually, as shown here, crystals much larger were produced. The pictures shown are of calcium oxide crystals, which do not exist in nature, since they are hygroscopic, and are destroyed by the humidity in the atmosphere in a m a t t e r of hours. Crystals of aluminum oxide, calcium oxide, magnesium oxide, hafnium oxide, titanium carbide, and titanium diboride have been grown and some of their physical properties determined. I t was thought t h a t the raw material had to be rather pure but it was found t h a t the initial purity determined only the time required for the process. Impure materials had to be heated longer in the solar fm'nace to allow the impurities to vaporize or to diffuse into the cooler regions of the melt. To demonstrate this point, when calcium sulfate crystals were heated in the solar furnace, calcium oxide crystals were grown inside them, Fig. 14. The sulphur escaped as SO.~, the water v a p o r as steam H2 and ()2 as gases. Vol. 8, No. 1,1964
FIG. 14--CaSO4.2H~O crystals (bottom), after irradiation with CaO crystals inbedded (top). The work described above demonstrated t h a t the solar furnace can be used to grow crystals of useful sizes by the vapor deposition process, and, better still, by the puddle melt method. Rather impure materials can be used as raw materials and can be in powder, rock, or crystal form. Thus it seems that a solar furnace could contribute greatly in helping to reach the objectives of ~ lunar station.
ACKNOWLEDGMENTS Tile author wishes to express his t.hanks to: Mr. W. L. Freeman, Mr. R. K. Chari, and graduate students and st.udents for 41
their help with this project and other work at tile Solar Energy L a b o r a t o r y of the University of Florida. To l)r. G. Hughes and ])r. E. F. Sieklnann and Airman J. I). R i t t s while p a r t of tiffs work was carried out at the D i r e c t o r a t e of Research Analyses, Air Force ONce of Scientific Research, Office of Aerospace Research, United States Air Force, Holloman Air Force Base, New Mexico. To Ranger R. Morris of the White Sands N a t i o n a l Monument, who took a group to Lake Lucero in the s()utheast region of the White Sands M o n m n e n t in collect C'~SO4.2H20 crystals, later used in this work.
Letters to the Editor CONSTANCY OF THE SOLAR CONSTANT In the paper on the " I n t e r n a t i o n a l Years of the Quiet S u n " , SOLAR E N E R G Y Vol. 7, No. 4, 1963, p. 158 there is the statement, " A b b o t ' s work indicated t h a t , w i t h i n the precision of his observations, the solar c o n s t a n t is c o n s t a n t . " This is not the case. See m y paper "Solar Variation and W e a t h e r " (Smith Misc. Coll. Vol. 146 No. 3 Oct. 18, 1963 Pub. 4545)* of which a copy is being sent to you. Its Section 1 " T h e solar c o n s t a n t " Table 1, page 13, with accompanying text, proves the contrary. This Table 1 rests on 1992 comparisons, between 4 i n d e p e n d e n t stations, of pairs of daily solar c o n s t a n t determinations. The pairs of stations are thnllsands of miles apart, in b o t h hemispheres, observing at all seasons of the year, from altitudes of 5000 to 10,000 feet. No a p p a r e n t general discrepancies are discernable as to altitude, hemisphere, time of the year, or water vapor content of the atmosphere. M a n y other kinds of evidence of real solar variations are explained and graphically presented in "Solar Variation and W e a t h e r . " And it i~ associated with p h e n o m e n a of ionospherics, hurricanes, nmgnetic storms, precipitation, temperature, h u m a n pulse, sunspots, calcium flocculi, as a b u n d a n t l y shown in Pub. 4545, hut which would be shown m a n y times as m a n y cases from accurate studies, of which the Smithsonian I n s t i t u t i o n at Washington preserves records over past 60 years. Above all, there is u n d o u b t e d l y a family of regular periods in solar variation, all harmonics of exactly 273 months. See pages 60 to 63 of Pub. 4545, and Figure 29 associated therewith. See besides Figures 10, 11, 18, 20, 23, 24, 25, 26, 27 of Pub. 4545. * E d i t o r ' s Note: Smithsonian I n s t i t u t i o n publication 4545 1)r. A b b o t refers to contains an interestingly written, well referenced account of the work done from 1920 to 1955 with the aid of J o h n A. Roebling, the Smithsonian Astrophysical O b s e r v a t o r y under his direction in making solar-constant observations. It also includes a summary of work done by others, beginning with Pouillet and his invention of a pyrheliometer in 1876. It Mso has a section of "Periodicities in Solar V a r i a t i o n " , one on "Solar Variation and W e a t h e r " , and concludes with an extensive discussion of long range weather prediction t h a t Dr. A b b o t mentions in his letter. P u b l i c a t i o n 4545 is available from tile Smithsoni,m I n s t i t u t i o n , Washington, D. C.
42
To Dr. P. D. Jose, Director of the D R A Scientific Laboratory, and to l)r. G. R. E b e r , Chief of SRAS.
REFERENCES The published i n f o r m a t i o n related to this project is found in three groups of papers : A - - T h e Proceedings of the 1955 World Symposium on Solar Energy, held in Phoenix, Arizona B The Proceedings of the 1957 Solar Furnace Symposium, held in Phoenix, Arizona. (20 papers). C - - T h e 1962 U. N. Conference on New Sources of Energy, held in Rome, Italy. (12 papers on Solar Furnaces).
While the solar harmonic variations of 273 m o n t h s range only between 0.02 and 0.03 of one percent of the solar constant, the identical period harmonies in terrestrial precipitation range from 5 to 45 icereent of normal precipitation. But these are hidden from cursory inspection by phase changes associated with time of the year, prevalence of sunspots and population changes which affect the atmosphere. Mr. J o n a t h o n Wexler, with an electronic computer, has recalculated from published "World Weather Records" 222 tables per s t a t i o n which permit us to eliminate largely those phase effects at each of 54 weather stations in U.S., Europe, Asia, Africa, Australia, and South America, which Mr. Hill and I have studied already. We have been able thereby to forecast precipitation for as n m c h as 60 years in advance. M a n y graphs of such forecasts are shown in Pub. 4545. For 32 U. S. stations, see Pub. 4390. CHARLES G. ABBOT Hyattsville, M a r y l a n d
T H E ICE M A K I N G M A C H I N E I have read with interest the correspondence regarding icemaking machines. It was of particular interest, to me to read in the Oet./1)ee. issue of the use in I n d i a of the Carr6 type ammonia ice making machine. I have a copy of the l l t h edition of G a n o t ' s Physics (1883),t t r a n s l a t e d from the F r e n c h in 1863, which describes this machine and also a very simple sulfuric acid a p p a r a t u s for freezing water. Some of your readers may be interested in this reference. FRANCm P. GmFF~THS Chemist in Charge Agricultural Research Service, USI)A. Weslaeo, Texas E d i t o r ' s N o t e : F. Griffiths t h o u g h t f u l l y provided a photoslat copy of the sections mentioned in the G a n o t ' s "physics". In the section on p. 314 under the heading "Cold due to evaporation. Mercury frozen", the experiments of Leslie employing this principle is described in detail with a wood-cut drawing of his apparatus. It also mentions similar work by others: Wollaston, Richardson, and Harrison. M, Carrd's freezing of water by the distillation of ammonia is also discussed. Woodcut pictures of his a p p a r a t u s are shown, and details given of vari-ous models built by him. I t also describes a sulphuric-acid system employed by Carr5.
Solar Energy
REAT emphasis is put on space exploration today and experts believe t h a t one of the first tools available on the moon will be a solar furnace. One phase of our solar energy work has been to investigate ways in which a solar furnace could be used by a lunar station in support of its objectives. Things which can be done on the moon or extracted from lunar materials could eliminate transportation from the earth to the moon, an expensive, and timeconsuming process. T o d a y ' s best available sources regarding the most abundant materials to be found on the moon give O2 and H2 in compound form, Si, Fe, Mg, A1, Ca, etc. On the basis of this information the following objectives have been formulated: A - - T o extract water from simulated lunar materials, then to dissociate this water into hydrogen and oxygen, which can be stored as fuel and used at a later date by recombination. B - - T o grow crystals from simulated lunar materials and by a study of these crystals and their properties to obtain a better understanding of the fundamental nature of matter.
G
Manuscript received June 10, 1963.
FIG. 1--Solar furnace in operation 38
C - - L a t e r , if desirable, to take some of these crystals and by doping them change their characteristics as to produce "solar cells" for direct conversion of solar energy into electricity or optical masers for communication. This paper discusses the first part of objective B, the growing of crystals. A number of the crystals grown in the solar furnace at the University of Florida Solar Energy Laboratory, Fig. 1, are believed to be the first ones of their kind.
FIG. 2--Targets : can (left) ; pellet (right).
FIG. 3--Target irradiated in furnace ! No.a~ Energg
To produce these crystals, targets were prepared from materials in powder form (believed to be the state of matter on the surface of the moon). The powders were either put into cans with plastic or crystal glass covers to keep the powders from falling out, or pressed and sometimes sintered into pellets, eliminating the container all together. Fig. 2. When these targets are irradiated in the solar furnace, Fig. 3, the powder melts and fuses, forming a liquid puddle within which, upon cooling, crystals are found. A crater develops and becomes deeper the longer the sample is irradiated. In some cases the crater was repacked with powder periodically to increase the size of the melt, which, in turn, had a direct bearing on the size of the crystals produced. Crystals l~ cm in length and about 0.5 cm thick have been grown in this man-
FIG.
ner. Some difficulty was experienced in getting the crystals out of the melt in one piece. Another method used successfully was vapor deposition. A crater was burned into the target in the above manner. Then only one side of the crater was heated with the vapors produced made to stream over the cool edge of the crater on the other side. By this method vapors condensed and formed perfect crystals. These vapor-deposited crystals were smaller than tlle ones produced in the melt. hnpure materials could be used, inasmuch as during the heating, impurities vaporize or diffuse into the cooler regions or zones leaving pm'e and clear crystals. AfteR' removing the sample from the irradiating beam it cools, Fig. 4, and the crystals are formed and grown. Fig. 5 shows the cold crater with snmll crystals (about 2 mm on the side), looking like teeth in a mouth, near the center of the crater. Under longeR' irradiation a smooth bottom crater is formed, Fig. 6, and if repacked periodically a largeR' and thicker melt is produced. The outer regions of the target around a typical crater are not affected by the heat, thus, are still in powder form. Nearer the crater the powder is sintered due to the exposure to heat. Still closer to the crater small but perfect crystals are found, Fig. 7, formed by vapor deposition as explained above. These crystals become more numerous as the edge of the crater is approached and combine into some typical formations such as the "christmas trees" shown in Fig. 8. Names like these have been given to the most frequently observed formations to simplify discussion of them. The crater bottom itself is a smooth, thick, glassy
4--T~rget cooling
FIG. 5--Irradiated target, small crystals near center Vol. 8, No. 1, 19b'~
FI~. 6--Irradiated target, deep crater 39
FIG. 9
Crater b o t t o m
FIG. 7--CaO crystals, vapor deposition
FIG. 10--Large crystal inbedded in melt FIG. 8--CaO crystal formations near crater edge mass, Fig. 9, with cleavage lines visible between the individual crystals which formed during the cooling process. A large imbedded crystal is seen in Fig. 10. Often these crystals broke into smaller ones, splitting along their crystal faces, as they were pried from the melt. 40
When the melt is broken in half, the cross-section, Fig. 11, shows the crystals imbedded and with some of their faces exposed. The thicker the melt, a function of repacking repeatedly and irradiating for longer periods, the larger are the crystals produced. Larger CaO crystal pieces produced in the melt are shown in Figs. 12 and 13. They are about 5 mm in size. At the beginning of this work the minimum useful Solar Energy
FIG. ll--Crater bottom cleavage, inbedded CaO crystals
FIG. 13--CAO crystal twins, perfect optical quality, (5 mm)
FIG. 12--CAO crystal fragment, perfect optical quality, (3 mln) crystal size was set at 1 m m on a side. This seemed to be the minimum crystal size necessary for the deterinination of the physical properties. Actually, as shown here, crystals much larger were produced. The pictures shown are of calcium oxide crystals, which do not exist in nature, since they are hygroscopic, and are destroyed by the humidity in the atmosphere in a m a t t e r of hours. Crystals of aluminum oxide, calcium oxide, magnesium oxide, hafnium oxide, titanium carbide, and titanium diboride have been grown and some of their physical properties determined. I t was thought t h a t the raw material had to be rather pure but it was found t h a t the initial purity determined only the time required for the process. Impure materials had to be heated longer in the solar fm'nace to allow the impurities to vaporize or to diffuse into the cooler regions of the melt. To demonstrate this point, when calcium sulfate crystals were heated in the solar furnace, calcium oxide crystals were grown inside them, Fig. 14. The sulphur escaped as SO.~, the water v a p o r as steam H2 and ()2 as gases. Vol. 8, No. 1,1964
FIG. 14--CaSO4.2H~O crystals (bottom), after irradiation with CaO crystals inbedded (top). The work described above demonstrated t h a t the solar furnace can be used to grow crystals of useful sizes by the vapor deposition process, and, better still, by the puddle melt method. Rather impure materials can be used as raw materials and can be in powder, rock, or crystal form. Thus it seems that a solar furnace could contribute greatly in helping to reach the objectives of ~ lunar station.
ACKNOWLEDGMENTS Tile author wishes to express his t.hanks to: Mr. W. L. Freeman, Mr. R. K. Chari, and graduate students and st.udents for 41
their help with this project and other work at tile Solar Energy L a b o r a t o r y of the University of Florida. To l)r. G. Hughes and ])r. E. F. Sieklnann and Airman J. I). R i t t s while p a r t of tiffs work was carried out at the D i r e c t o r a t e of Research Analyses, Air Force ONce of Scientific Research, Office of Aerospace Research, United States Air Force, Holloman Air Force Base, New Mexico. To Ranger R. Morris of the White Sands N a t i o n a l Monument, who took a group to Lake Lucero in the s()utheast region of the White Sands M o n m n e n t in collect C'~SO4.2H20 crystals, later used in this work.
Letters to the Editor CONSTANCY OF THE SOLAR CONSTANT In the paper on the " I n t e r n a t i o n a l Years of the Quiet S u n " , SOLAR E N E R G Y Vol. 7, No. 4, 1963, p. 158 there is the statement, " A b b o t ' s work indicated t h a t , w i t h i n the precision of his observations, the solar c o n s t a n t is c o n s t a n t . " This is not the case. See m y paper "Solar Variation and W e a t h e r " (Smith Misc. Coll. Vol. 146 No. 3 Oct. 18, 1963 Pub. 4545)* of which a copy is being sent to you. Its Section 1 " T h e solar c o n s t a n t " Table 1, page 13, with accompanying text, proves the contrary. This Table 1 rests on 1992 comparisons, between 4 i n d e p e n d e n t stations, of pairs of daily solar c o n s t a n t determinations. The pairs of stations are thnllsands of miles apart, in b o t h hemispheres, observing at all seasons of the year, from altitudes of 5000 to 10,000 feet. No a p p a r e n t general discrepancies are discernable as to altitude, hemisphere, time of the year, or water vapor content of the atmosphere. M a n y other kinds of evidence of real solar variations are explained and graphically presented in "Solar Variation and W e a t h e r . " And it i~ associated with p h e n o m e n a of ionospherics, hurricanes, nmgnetic storms, precipitation, temperature, h u m a n pulse, sunspots, calcium flocculi, as a b u n d a n t l y shown in Pub. 4545, hut which would be shown m a n y times as m a n y cases from accurate studies, of which the Smithsonian I n s t i t u t i o n at Washington preserves records over past 60 years. Above all, there is u n d o u b t e d l y a family of regular periods in solar variation, all harmonics of exactly 273 months. See pages 60 to 63 of Pub. 4545, and Figure 29 associated therewith. See besides Figures 10, 11, 18, 20, 23, 24, 25, 26, 27 of Pub. 4545. * E d i t o r ' s Note: Smithsonian I n s t i t u t i o n publication 4545 1)r. A b b o t refers to contains an interestingly written, well referenced account of the work done from 1920 to 1955 with the aid of J o h n A. Roebling, the Smithsonian Astrophysical O b s e r v a t o r y under his direction in making solar-constant observations. It also includes a summary of work done by others, beginning with Pouillet and his invention of a pyrheliometer in 1876. It Mso has a section of "Periodicities in Solar V a r i a t i o n " , one on "Solar Variation and W e a t h e r " , and concludes with an extensive discussion of long range weather prediction t h a t Dr. A b b o t mentions in his letter. P u b l i c a t i o n 4545 is available from tile Smithsoni,m I n s t i t u t i o n , Washington, D. C.
42
To Dr. P. D. Jose, Director of the D R A Scientific Laboratory, and to l)r. G. R. E b e r , Chief of SRAS.
REFERENCES The published i n f o r m a t i o n related to this project is found in three groups of papers : A - - T h e Proceedings of the 1955 World Symposium on Solar Energy, held in Phoenix, Arizona B The Proceedings of the 1957 Solar Furnace Symposium, held in Phoenix, Arizona. (20 papers). C - - T h e 1962 U. N. Conference on New Sources of Energy, held in Rome, Italy. (12 papers on Solar Furnaces).
While the solar harmonic variations of 273 m o n t h s range only between 0.02 and 0.03 of one percent of the solar constant, the identical period harmonies in terrestrial precipitation range from 5 to 45 icereent of normal precipitation. But these are hidden from cursory inspection by phase changes associated with time of the year, prevalence of sunspots and population changes which affect the atmosphere. Mr. J o n a t h o n Wexler, with an electronic computer, has recalculated from published "World Weather Records" 222 tables per s t a t i o n which permit us to eliminate largely those phase effects at each of 54 weather stations in U.S., Europe, Asia, Africa, Australia, and South America, which Mr. Hill and I have studied already. We have been able thereby to forecast precipitation for as n m c h as 60 years in advance. M a n y graphs of such forecasts are shown in Pub. 4545. For 32 U. S. stations, see Pub. 4390. CHARLES G. ABBOT Hyattsville, M a r y l a n d
T H E ICE M A K I N G M A C H I N E I have read with interest the correspondence regarding icemaking machines. It was of particular interest, to me to read in the Oet./1)ee. issue of the use in I n d i a of the Carr6 type ammonia ice making machine. I have a copy of the l l t h edition of G a n o t ' s Physics (1883),t t r a n s l a t e d from the F r e n c h in 1863, which describes this machine and also a very simple sulfuric acid a p p a r a t u s for freezing water. Some of your readers may be interested in this reference. FRANCm P. GmFF~THS Chemist in Charge Agricultural Research Service, USI)A. Weslaeo, Texas E d i t o r ' s N o t e : F. Griffiths t h o u g h t f u l l y provided a photoslat copy of the sections mentioned in the G a n o t ' s "physics". In the section on p. 314 under the heading "Cold due to evaporation. Mercury frozen", the experiments of Leslie employing this principle is described in detail with a wood-cut drawing of his apparatus. It also mentions similar work by others: Wollaston, Richardson, and Harrison. M, Carrd's freezing of water by the distillation of ammonia is also discussed. Woodcut pictures of his a p p a r a t u s are shown, and details given of vari-ous models built by him. I t also describes a sulphuric-acid system employed by Carr5.
Solar Energy