FULGURITE AND ITSARTIFICIAL PRODUCTION

IN LABORATORY

by K.KUMAZAKIINTERNATIONAL COLLEGE OF TECHNOLOGY

K. NAITO, K. NAKAMURANAGOYA INSTITUTE OF TECHNOLOGY

K.HORILYOYODA COLLEGE OF TECHNOLOGY

( JAPAN )

ORIGINALLY PUBLISHED IN

8TH INTERNATIONAL SYMPOSIUMON HIGH VOLTAGE ENGINEERING

PROCEEDINGS VOLUME 3YOKOHAMA, JAPAN AUGUST 23-27, 1993

ORIGINALLY PUBLISHED IN

8TH INTERNATIONAL SYMPOSIUMON HIGH VOLTAGE ENGINEERINGPROCEEDINGS VOLUME 3YOKOHAMA, JAPAN AUGUST 23-27, 1993

FULGURITE AND ITSARTIFICIAL PRODUCTION

IN LABORATORY

by K.KUMAZAKIINTERNATIONAL COLLEGE OF TECHNOLOGY

K. NAITO, K. NAKAMURANAGOYA INSTITUTE OF TECHNOLOGY

K.HORILYOYODA COLLEGE OF TECHNOLOGY

( JAPAN )

ABSTRACT

In an ISH 93 companion paper, the authors described theirsuccess in the production of fulgurite by artificially-triggeredlightning. In this paper, authors describe their effort and suc-cess in the production of fulgurite in a high voltage laboratory.In the present study, natural river sand was filled up in a con-tainer and lightning impulse currents of various magnitudeswere passed through it which were supplied from an impulsecurrent generator. It is believed that this is the first success inlaboratory production of fulgurite in the world.

INTRODUCTION

A fossil of thun-derbolt was discov-ered in Germany in1706, and the fossilwas identified byWithering in 1709[1]. Harland, et al.found a red-colorsandstone in Arranaeolian deposit inScotland [2]. Itseems that thefulgurite was pro-duced by lightningstriking in thedesert in the Per-mian period of thePalaeozoic era,about 2.5 millionyear ago. Figure1(a) is the photo-graph of the fulgurite fossil. As seen in the photograph, thepart of the fulgurite made of quartz glass has been satisfactorilypreserved, having been withstanding the weathering. The hol-low portion in the central position was scraped off.

In most cases, natural lightning-striking is accidental inde-pendently of time, places, and materials. Accordingly, it is onlythrough the artificial production of fulgurite that the processand mechanism of it can be known. Some more explanation ismade in a companion paper [3].

(a) Photograph of fulgurite fossil 250 milllon years ago

(b) Sketch view of fig.1(a), upper: transversal section,lower: radial section

Figure 1: Fulgurite fossil

Figure 2: Cross-sectional view of fulgurite

raw materialraw material sticking partCristobalite - conversion partLechatierite - conversion parthollow part

ARTIFICIAL PRODUCTION OF FULGURITE

At any rate, the following conditions will be required for theproduction of the fulgurite:

- Huge electromagnetic energy is supplied for a very shorttime, in the order of microsecond, so that the soil and sand, orrocks are vitrified;

- Principally, the fulgurites take a cylindrical shape, having ahollow portion which is a trace of the streamer passing through;After the passage of the streamer, the hollow portion is some-times filled with a melted substance;

- As outlined in Fig. 2, the cross-section of the fulgurite issubstantially concentric: In the concentric cylinders of the fulgu-rite, the next outer part is done of striking raw material, andthe outer most part is remained raw material; These materialsare present in the circular range with a radius of several cm andsometimes with a diameter of 15 - 16 cm. Such constitutionscan not be produced by any other means.

For completely artificial production, the following materialswere prepared:

(1) river sand (Tempaku River): The reasons for the use arethat the river sand is natural without being processed, and thatit can be conveniently obtained.

(2) fluorite powder: Fluorite belongs to a cubic system, sothat the refractive index after the convention can be easily de-termined.

epyTniargmmezis 01.91 25.9 67.4 00.2 48.0 24.0 52.0 501.0 470.0

ssel470.0

esraoc .0 47.0 79.44 12.45 31.0 11.0 11.0

elddim .0 09.51 23.87 18.2 78.1 97.0 13.0

enif .0 43.91 62.25 90.71 03.01 89.0 30.0

elddim .0 73.72 64.95 81.5 49.2 28.1 03.0 39.2

enif .0 58.0 08.73 86.24 19.9 81.5 96.0 98.2

epyTniargmmezis 00.2 48.0 24.0 52.0 501.0 470.0 150.0 730.0 520.0 510.0 110.0

ssel110.0

esraoc .0 21.0 38.31 57.05 68.23 90.2 53.0

elddim .0 51.0 34.33 83.2 22.91 59.3 26.21 13.12 75.1 73.5

Sab sand

Tempaku riversand

Silica sand

Table 1: Grain size distribution of material for production of fulgurite.

Residual rate % unit

(3) silica sand: Natural sandcontains a mixture of a varietytype of minerals. The sand wasselected for the purpose of ana-lytical experiment (Si0 about95%).

(4) Saba sand: During the ex-periment, saba sand contains alarge amount of feldspar of whichthe melting point (l200 - 900 C)is lower than quartz.

(5) polyethylene: During theexperiment, polyethylene particles of which the melting pointis much lower was used to know the state of streamers.

It was estimated that the grain size of the materials wouldexert an influence over the fulgurite production. The grain sizewas classified into three groups, that is, coarse, middle, andfine grain groups as shown in Table 1.

The following devices are prepared for the experiments:(1) Sample Container: High strength and dielectric strength

are required to prevent the container from being broken whenapplied with voltage and mechanical pressure. An ebonite platewas used at the bottom of the container. The distance betweenthe electrodes was adjustable within the range of 10 - 80 mm.Figure 3 shows shape and size of the container, and the volumeof it was about 2000 cc.

(2) Impulse Current Generator: Several different impulsevoltage generators were used. The largest generator used hada maximum charging voltage of 3600kV. For the experiment,first, an impulse voltage of 14kV was used. Then, the voltagewas gradually increased. As described below, the impulse volt-age generators were modified into impulse current genera-tors. Figure 4 illustrates a typical generator circuit used in thepresent study.

Experimental procedures were as indicated below. First, fill-ing the container with raw materials. In the study, the stan-dard impulse voltage wave 1x40 microsecond was used. Therewas thus some difference in the wave form between the test

Figure 3: Container of material forthe production of fulgurite

voltage used this time and that of typical cases of the travelingwaves of actual thunders, whose total duration and the wavefront are, 100 microseconds or so, and about 1 - 10 microsec-onds, respectively.

At first, the impulse voltage was applied to one sample at atime, but fulgurite could not be produced. Then, the impulsevoltage was repeatedly applied 5 - 3 times.

In the total 84 cases of the experiment, there was observedsubstantially no conversion to fulgurite in the 1 - 44th cases. Inthe 45th or latter cases, fragments of fulgurite became to ap-pear. Thus, the number of application of impulse voltage wasfound very important.

As seen in Table 2, simple increase in voltage did not resultin the production of fulgurite. Thus, the generator circuit wasmodified: the capacitors were connected in parallel so that thecurrent intensity could be increased.

Main points of the experimental results were as follows. Alonga streamer of onion-like shape traveling between the electrodes,a spherical, hollow, dark brown, fragile fulgurite was producedwhich had a sea-urchin-like rough surface in appearance. Thediameter was about 4 cm, the height was 2 - 4 cm. A greatattention should be paid to the relation between the voltageapplication number and the production of fulgurite, in order

Figure 4: Circuit diagram for production of fulgurite in laboratory

to prevent theshell-shape fulgu-rite from beingbroken - SeeFig.6(a)(b).

Table 3 sum-marizes the ex-perimental re-sults of the rela-tion obtained at acurrent rangingfrom 0.01kA to15kA and a volt-age from 10kV to600kV. The results were discussed, based on the fulgurite in-cluding partial product of it. All the products seemed ratherfragile. This may be attributable to the low current comparedto the natural lightning current. For the production of fulgu-rite, a current of 50 kA or higher seems necessary although a

VK/AK 02~01 05~12 001~15 006~101 latoT %etarnoitcudorP

10.0 03 0 03 52.6

1.0~ 0 2 2

11.0 9 9 0

0.5~ 0 0

1.5 0 1 1 8.39

0.01~ 2 31 51

1.01 4 0 4 2.58

0.51~ 91 4 32

latoT 03 4 1 9 44

0 12 91 0 04

noitcudorP%etar 0 0.48 0.59 0

Figure 5: Waveform of impulse current for production offulgurite

Time marker: 500kHz

Table 2: Test Parameters and resultsUpper line: number of case of no productionLower line: number of case of successful production

high voltage is not necessarily needed. Thus, a generator of ahigh energy is preferred. Provided that the generated energiesare equal, a higher current is favorable for the production offulgurite.

The influence of the selection of materials on the produc-tion is of interest. In the case of Saba sand, the production ratiois highest, that is, 100%. The Tempaku River sand has the nexthighest production ratio of 84X. For the silica sand which ispurest, the ratio is low, e.g., 7.25 as seen in Table 3. As for thegrain size, the fine grain of the Tempaku River sand and themiddle-sized grain of the Saba sand had a relatively high pro-duction ratio. As a whole, no significant difference was foundbetween the grain sizes.

Next, relation between discharge time and production offulgurite is of interest. The extent of fulgurite production wasdivided into four stages. The experimental results of the rela-tion were summarized, depending on the materials and the dis-charge time. In the case of the discharge time of 20 - 50 micro-seconds, a largest amount of fulgurite was produced.

As a trial, the discharge test was conducted for 1 - 2 millisec-ond, giving no successful results. For the silica sand, substan-tially no fulgurite was produced.

Relation between Energy and production of fulgurite wasexamined. In the range of 5,000 - 50,000 Joule, the produc-tion frequency was highest. When evaluated as a whole, basedon the above results, the energy required shall be at least 5,000J, and for more complete production of fulgurite, 10,000 J orhigher is favorable.

(a) produced from Tempaku river sand (b) produced from Saba sandFigure 6: Fulgurites produced this time

When the current intensity is increased, the production pos-sibility is increased. The discharge time of 20 - 50 microsecondis preferable. In the case of the generators used in the presentstudy, silica sand containing feldspar and so forth gave a highproduction ratio than that composed of quartz only.

An X-ray analysis was made. Namely, the Saba sand beforeand after the voltage application was compared. For most ofthe feldspar as well as all the quartz, the reflectivities were re-duced. The produced fulgurites were observed with a micro-scope for minerals. Substantially no changes in quartz werefound, while the peripheries of the feldspar grains were vitri-fied.

Accordingly, for production of fulgurite, silica sand contain-ing feldspar and so forth such as Saba sand, Tempaku Riversand, etc. is preferable to that made of quartz only.

CONCLUSIONS

- The artificial production of fulgurites has been realized inthe present study. The authors think that this is probably thefirst to describe the artificial production of fulgurite.

lairetaMwaR noitcudorP-noN

noitcudorplatoT %etarnoitcudorP

enelyhteyloP 0 8 8 0 0

etiruolF 0 8 8 0 0

abaSdnas

esraoc 2 0 2 001

001elddim 1 0 1 001

enif 5 0 5 001

aciliSdnas

elddim 2 8 8 0.522.71

enif 3 81 12 3.41

ukapmeTdnasrevir

elddim 8 2 01 0.080.48

enif 31 2 51 7.68

latoT 43 44 87

Table 3: Materials used and results

- New classification of fulgurite: fulgurites are not a simpleproduct by nature. It is necessary to classify such fulgurites intothree types; that is, natural, semi-natural and artificial fulgu-rites. Also, conventional classification of two types, dependingon materials of soil and stone, and rock, is necessary.

- Importance of the accumulation of information: It is need-less to say that thunderbolts are natural phenomena and arealmost impossible to foresee the event. Thus, it is important togather as much information as possible relating to the actuallightning strike.

- Future investigation of fulgurite: The following will be in-vestigated and revealed; as for natural fulgurites: (1) discoveryof fulgurites in as many countries possible, (2) historical, geo-logical and palaeozoic meteorological significance of fulguritesand the values as faces fossil, (3) relation between the remainedmagnetism of lightning-striking products, especially basic rocksand stones and lightning current; and as for artificial fulgurites:(1) elucidation of production mechanism and conditions, (2)the production of crystallite by devitrification, (3) depositionof free silicon, and so forth.

REFERENCES

[1] J. D. Dana and E. S. Dana. “The system of mineralogy”,pp. 321 - 324, John Wiley and Sons, Inc.

[2] W. B. Harland and J. F. Hacker. “Fulgurite”, Advance-ment of Science, pp. 663 -665, April, 1966.

[3] K. Kumazaki, K. Nakamura, K. Naito, K. Horii. “Fulgu-rite and its artificial production in laboratory”, ISH 93 Paper,1993.

ADDRESS OF AUTHOR

Prof. K. KumazaklInternational College of Technology1-15-1, Marunouchi, Naka-ku, NagoyaJapan

THE EVENT

PETRIFIED LIGHTNING FROM CENTRAL FLORIDA

A PROJECT BY ALLAN MCCOLLUM

CONTEMPORARY ART MUSEUMUNIVERSITY OF SOUTH FLORIDA

MUSEUM OF SCIENCE AND INDUSTRYTAMPA, FLORIDA