IE44592B1 - Improvements relating to photochromic glasses - Google Patents

Abstract

Fast-response alumino-phosphate photochromic glasses having silver halide crystals dispersed throughout the glass comprise, in weight percentages: SiO2 8.5 to 25% Al2O3 13 to 36.5% P2O5 7.5 to 33.5% B2O3 7 to 28% R2O 7 to 20.5% where R2O represents at least one of Na2O, K2O and Li2O, the maximum content of Li2O being 5%; the amount of SiO2 is not less than 16% when the B2O3 content is less than 8%; and the silver content of the glass, expressed as Ag2O, is not less than 0.05% by weight. Such glasses in which Al2O3 is the largest constituent are preferred for ophthalmic purposes, but it is also possible for either B2O3 or P2O5 to be the largest constituent. The glass can also contain 1% to 21% by weight R'O where R'O represents MgO, CaO, SrO or BaO. The refractive index can be corrected by nD = 1.523.

Description

This invention relates to photochromic glasses, i.e. to glass compositions which darken on exposure to actinic radiation and fade hack to their original, normally r , t colourless, state when no longer exposed.

In British Patent Specification No. 1,367,903, vie have described and claimed a range of photochromic glasses comprising at least 17% by weight ^2θ5 as one of the glaps forming components, with, silver halide crystals dispersed throughout the glass, the total silver ί content of the glass being at least 0.05% by weight Ag.

The specific glasses disclosed in that Specification are alumino-phosphate glasses comprising not more than 40% by weight SiO2 and between 9% and _ 34% by weight AlgO^ as further glass forming components, and at least 10% by weight RgO, where R=K, Na or Li. They can also contain up to 19% by weight Β2θ3’ though most of the glasses disclosed contain no more than 3 to 7% BgOy Glasses falling within the claims of British Patent 1367903 are now used in, the manufacture of ophthalmic lenses for both sunglasses and prescription spectacles.

These, alumino-phosphate glasses, like the photochromic borosilicate glasses also available in the market, while exhibiting desirable photochromic properties, have relatively slow responses to exposure and removal of actinic radiation, i.e. slow darkening and fading rates. It is desirable, particularly for ophthalmic purposes, to have glasses with faster responses, particularly a faster fading rate. A rapid fading rate is desirable to aid' in adjustment to a sudden decrease in available light, such as when a wearer of spectacles with lenses of photochromic glass enters a dimly-lit room. - 2.i 9 2 An object of the present invention is to provide a range of photochromic glasses having improved properties and, in particular, glasses which provide an improved combination of photochromic effect (measured as the induced optical density or change in light transmission when irradiated with actinic radiation) and speed cf response to irradiation or removal of radiation.

According to the present, invention, a photochromic aluminophosphate glass naving silver halide crystals dispersed throughout the glass comprises, as non-photochromic components in weight percentages: SiO2 8.5 to 25% Λ1?03 13 to 36.5P2°5 7.5 to 33.B2°3 7 to 28% R,0 7 to 20.5% % where E^O represents one or more of Na20, K20 and Li20, the maximum content of Li20 being 5%; the amount of SiO2 is not less than 16% when the B2°3 content is less than 61; and, as photochromic components, expressed as weight percentages over and above the 100% total of all the non-photochromic components of the glass: silver, expressed as Ag2O not less than 0.05% Cl+Br 0.20 to 2%.

These glasses have been found to have a good combination of induced optical density on irradiation with actinic light and rapid darkening on irradiation and rapid fading when irradiation ceases. It will be understood that, as a general rule, the darkening and fading times are longer when the induced optical density is greater.

In these glasses, it is possible for AljO-j, F^O^, or to be the largest constituent. The preferred range of glasses for ophthalmic purposes is that in which the largest constituent is AlgO- which is present in an amount of not less than 22 weight 5=, while the content of ?2°5 does not exceed 25.5 weight 5= and the content of does not exceed. 24.5 weight 5ό. Glasses within this preferred range can he formulated to have a fast response to irradiation or the removal of irradiation, coupled with physical properties which make them suitable for manufacture on a commercial scale and for use as ophthalmic lenses.

For example5 the liquidus temperature and viscosity of the molten glass can be chosen to suit conventional forming processes, while the hardness of the glass is appropriate for conventional grinding and polishing processes . The refractive Index can be adjusted to the standard value of 1.523 which is conventional for ophthalmic use, and the glass can have a good chemical resistance or durability.

In general, it is only practicable to operate with contents of both Α120^ and Si02 at the upper ends of the ranges set out above in cases where a high viscosity Is » required at the liquidus temperature, which itself is not too high, for example where the glass is to be formed into sheet glass.

Another range of glasses within the scope of the present invention is that wherein the largest constituent is which is present in an amount of not less than weight ?£, while the content of Al^O^ does not exceed Weight % and the content of ?2®5 does not exceed 20 weight ϊί, A further range of glasses according to the present invention is that wherein the largest constituent is which is present in an amount of not less than 21.5 weight 50, while the content of AlgO^ does not exceed 26 weight 5= and the content of B20^ does not exceed 17.5 Weight 5«, - 4 4 4 5 9 2 If the liquidu;. temperature ic made relatively low, e.g. as a result of the use of a relatively large amount of and a relatively small amount of SiC2, it is important to keep a watch that the durability of the glass (e.g. as tasted by absence of attack in acid and alkali solutions) is still acceptable. The degree of durability which is acceptable will of course vary according to the proposed use of the glass. Thus a glass which has insufficient durability for ophthalmic Ιϋ use but good photochromic properties may be of value for use in instruments or other uses where it is not exposed to attack.

When the B20^ level approaches the lower limit, i.e, is less than 8%, it is necessary that the Si02 conit tent is at least 16% in order to ensure both the desired fast response and adequate durability for ophthalmic purposes. fhjO may be constituted solely by KgO, or by a combination of two or more of K20, Li20 and Na20, or by 2Q Na20 alone. Where R20 is Na20 alone, it should preferably not exceed 14% by weight, to avoid possible problems in glass forming and durability.

In the case of glasses intended for ophthalmic use, it is advantageous for the glasses to be capable of being toughened by the conventional ion exchange process, in which larger metal ions are exchanged for smaller metal ions in a surface layer of the'glass to produce a compressive stress therein, The ion exchange is effected by immersing the glass in a molten salt bath. Generally potassium ions - 5 44592 arc exchanged for sodium and/or lithium ions in a bath of molten KNOg, or sodium ions are exchanged for lithium ions in a molten NaNOg bath. Thus where the glass is to be chemically toughened in this way it is preferred that the RgO component should include NagO and/or LigO. We prefer to use a mixture of alkali metal oxides, with KgO always present, and neither of NagO or LigO exceeding 5% by weight. The depth of penetration of the exchanged ions, and the compressive stress produced, can be varied by varying the temperature of the molten salt bath. In general, the greater the penetration, the lower the compressive stress and vice versa, so an advantageous compromise must be found by experiment.

As indicated above, the silver content of the glass, expressed as Ag2O, is not less than 0.05% by weight over and above the 100% total of all the non-photochromic components of the glass, because with lower amounts of AggO it can be difficult to achieve adequate darkening. Preferably the AggO is not less than 0.06% by weight over and above the 100% total of all the non-photochromic components of the glass.

The glass may further comprise as further non-photochromic components from 1 to 21% by weight R'O, where R'O represents at least one of MgO, BaO, SrO and CaO, within the following individual limits: Mgo 0 to 4% CaO 0 to 6.5% SrO 0 to 10% BaO 0 to 21% For ophthalmic use, it is convenient for the glass tc have a refractive index (nQ), measured for light of the wavelength of the sodium D line, which is as close as possible to the standard figure of 1.523. To adjust the refractive index to this figure, additions of proportions of TiOg, - 6 44592 ZrC>2 and/or PbO can be of value, though care is needed to avoid problems arising from too large a quantity of one or more of these components. These components are also considered to be non-photochromic. The amount of TiC^ used should not exceed 6% by weight, in order to avoid dangers of crystallisation and unwanted colouration of the glass, the normal preferred limit being 35. by weight. ZrO2 should not exceed 10 weight % in order to avoid unacceptable increases in liquidus temperature, the normal preferred limit being 7 weight 1 %. PbO can be incorporated in quantities up to 3% by weight. Small quantities of other additives, such as HfO2 (up to 3%) and ZnO (up to 6%) may be incorporated for the same purpose. Tinting agents may also be added in known manner, to provide a fixed tint in addition to the variable photochromic colouring.

As is known, the photochromic effect is produced by the silver halide crystals referred to above. Minor amounts of copper oxides assist the development of the photochromic effect, and larger amounts may be used to provide a fixed tinting effect in addition. The preferred amounts of the photochromic components, namely the silver (expressed as Ag20), the copper oxide and the halides (Cl and Br), •J 445®® . . which are expressed in accordance with the normal convention as quantities over and above the 100% total of ail the non-photochronic components of the glass, are as follows: Ag2O 0.06 to 0.60% > ' CuO 0.005 to 1.0% Cl 0 to 1.0% Br o.oa to i.o% ; In most cases, the photochromic effect can be enhanced by heat treatment of the glass, the appropriate heat treatment schedule being primarily determined by the viscosity-temperature relationship of the particular glass.

In general, the heat treatment temperature lies between the strain point and the softening point of the glass, the heat treatment time required being several hours at the lower temperature but only a few minutes at the higher temperature. At the higher temperature, however, deformation and clouding of the glass may occur, so it is preferred for convenience to use a temperature 20° to 100°C above the annealing point and a heat treatment time of 10 to 60 minutes. * The schedule may be imposed on the glass directly after forming or the glass may be annealed and cooled to room temperature before heat treatment. The cooling rate to which the glass Is subjected after heat treatment is sometimes fdund to have an effect on the photochromic properties of the final product. This cannot be stated as a general rule, however, and must be determined by experimentation on individual glasses.

The temperature/timo schedule imposed on a glass is also 30 determined by the concentrations of photochromic agents in - 0 44592 the class and the photochromic property requirements of the final product, in general, the higher the levels of the components contributing to the photochromism the shorter will be the heat treatment schedule, and in some case, the photochromism may develop during cooling from the melt or annealing of the glass. Excessively long heat treatments are generally to be avoided because they may lead to some clouding of the glass.

Specific embodiments of the invention will now bt described in more detail by way of example, and witn reference to the following Table I, which sets out examples- oi glass compositions in accordance with tne invention, shoving their compositions on.the oxide basis and the photochromic effect achieved in terms of the induced optical density (ODd) and the time in seconds taken to fade to a condition of half the total induced optical density (½ OD FT), measured with standard samples of glass mm thick, in standard simulated solar conditions at air mass 2 (see Parry Koon, J, Franklin Inst., 230 (1940), pages 583-617). The induced optical density is the difference between the optical density of the glass in the fully darkened state and the optical density in the fully faded, state, the optical density being defined in the conventional manner’ as logpo 7^ , where Ii is the intensity of the incident xt light and It is the intensity of the transmitted light.

The induced optical density is thus a real measure of the photochromic effect and is in fact directly proportional to the number of photochromically activated silver atoms in a given volume of the glass. The time required to fade from the fully darkened condition to a condition of half the induced optical density (-J OD FT) is thus an effective measure - 9 44592 for comparing fading times of glasses having different I values of light transmission in the hleachc-d or faded state and is comparable v/ith the half-fading times referred to in our British Patent Specification No. 1,367,903.

Table I.also lists the temperature (HT°C) at which each of the glasses was heat treated. A standard heat treatment time of 20 minutes was used in each caseB for comparative purposes only.

. Finally Table I lists the refractive-index n^ of ° most of the glasses. - 10 I r-j· ri in r I ri • o CM m »n CM b η <0 MO m r-i H CM cf> o> f, » • • • » t-1 If\ 1/ \ r-l -J • CM CM CM ri ri ri in in m o CM • • « • , • r-i OS H CM CM CM CM ri H H in b m MO CM • • * • o m in CM o CM CM co • CM n CM rl CM r-i CM CO CO O « • • 9 CM b b Ό -d « CM CM H r-i r-i H O v0 rn C ω • 0 • • « in b- OS b b σ’ H r-i CM OS ri O M0 n o 03 • • « • n is OS !S b Os rt ri (\J Os ri O V) tn o ω • « • • m • b 0s b b- 9 os r-t r4 CM os ri ! 4 45 9 2 us o Ί/ < m o O O o in ·< r 1 r! • • • 9 « 1 U 10 © o © © © US 00 »r\ i s fn © Γ) ri (.> CM CM ns t\l •M » • 9 β • \ * MO O © © O © o •*i ω in b MO OS o ri o CM CM o m • • • 9 • r- b © o O © © co MD CM m IS b MO in H σ ri CM o ob • • 9 • CM S O o O o o in co -j OJ CD <ϊ vo Ch MO ω r-i 00 • • • • ω b in H • o ri ri CM ri OS CM CM Ό σ· OS O • 9 « • • r-i in m r·! CM CM CM ri r-i i—i C\j Γ-Ι W vi « ft o r-d -a- m co in • 9 « 9 « ns o m fSJ (0 rn 9 CM CM m H r-i Is o m ri ns 9 • • • • -Μ- J—1 Os vO b CM ri CM r-i r-i η H OS ω CM in η rn os Mf) irs 9 CM ri ri CM r! r-i ri • ω 6 ω in T-< NS NS OS f\* b o m • CM ri t k (M ri ri TQ BLE tn mo ms 'co o O . 0 0 * · ‘ · ♦Η Η N CM tn <; m co u CM HO «1 ? id σ; u 10 ο ο (S £ c\j ο «ri Η OJ CM o o o U o σ. CM co CM rl o ri CSJ * u « « O © © o f—i -M* “2 c? rl o 9 • 9 • a © © © CM m OS OS H o 0 • * 9 O © © o CM s~-t m σ Η r—i o 4* o- 9 • 9 O © o o CM 10 m in <· H o m ♦ 9 • 9 O o o o CM m NS fn b- r-i ϋ H H 9 9 • 9 o o © o Os m rn b- CM o o r-i CM * « • • © © O o ω rl :n CM ro o o CM CM 9 0 9 9 © © o o s OS CM o ri C3 m -J· λ 4 O 6 o o b m ri n os (\J o rl m k a « u © o o o O CM O W) © r-i U < u Ο φ r-i b O o’ CM US O b ; ro i-a- H ffi rn O J Π m m O NS | 9 * (M 10 J r-i o OS Ό CM O in CM CM KS 1 · 9 r-i Ό 1 r-< © O MO Ch r-l US ri in CM CM m co © CO H to cn in ri m r 9 b MO ri © NS r-i ω M0 o CM o MO 9 β V MO ri O •d* (SJ OJ a O -J CM O i-n • • CM US ri O CM in CD CO o •d* CM O CM • 9 CM M0 H © n b »n O M· NS O ΙΜ • 9 CM m »4 O b o in N\ o :0 νθ ο ' • ι I ο ίΛ rl - - ο · K'V UJ . Γ-ί rl rf rl U fA CM CM ι—ί . -» (Α Η ιη (Μ » • » m ω ο\ rl if> CV •ί ιη η m tn ο ιη CM a β * CM CM tn co in Oj rl in cm CM CO cn tn 9 • • in co' d· tn o tn tn β 9 o « CM CM tn CO -t s rl O o o . CM 9 0 • CM * VO \O o m CM . u tn 9 9 CM CM m co rl in ΚΛ tn CM CM CM O s CO ω tn a a * •4* 9 (0 o CO H tA H CM CM H H co VO rt . <3* ό q 9 IS co rl a CM rl CM m s rl TABLE I (Continued) CO o VO r-j s <· • co H O 9 CM • H CM tn (S H cn • tn 6 rl o o CO 9 .in cn CM r-l 9 - CM . o ri CM tn CO K VO VO β co 9 <3- rl tn cn CM H 9 CM * rl CM m 00 rl in o o 0 o e CM CM ό VO o m CM o tn w CM tn co rl in S ri o e· o β o 9 CM w <0 o in CM 9 tA 9 CM cm m oo H tn VO rl- o O o CM * o -CM « VO o tn CM . m « CM CM tn co fH tn rl 0> Ol cn rl « 9 CM - · cn cn CM rl 9 tn 9 rl CM IA ω »rl m to w “ mJ O r-l U cm o m Ο (M c ' mo O CM o MO O o r-\ o e> CM O CM Cj CM O o 4> Ή r 1 M . CM -ri «1 M to . a» h (0 XI •rl ufK £ to * i ft tt r-l if ft £; o tn tt 5 t-4 N W KJ cn Ox m cn CO - I »-f n o O CM tn CM -4- ri • • • β c\5 ‘0 o 0 0 © © s ω t. \ 0 »n cn m O o 0 IA tn rl » 9 « • ♦ m vO © σ O 0 © cn rl •4 m m H in 0 o O CM h'\ CM cO r-l • 9 • * • rl VO © O 0 0 O in VO in 0 tn 0 O rl 0 K\ m CM GJ m • • » • • ri m © © O o, O cn 0- -4- 0\ 0 o a CM tn CM in s 9 ύ 0 « • rl vo o .© O © O s tn < rl •At H 0 o 0 in m rl m V) 9 0 a • β ?n VO o 0 O 0 0 co tn O CM VO *4* 0 o 0 tn tn rj CM rl • 9 » • O H V0 o s o 0 S' 0 m 0 in n cn m o 0 CM tn fl co rl 9 « 0 β rl V0 © O O 0 O s rl <1 S IS co O o ϋ CM in rl O rl 9 9 0 • » rl VO © © O 0 O s. in -:r a. •M in O CO O o O in m C M VO tn « 9 9 « β H vo o 0 0 0 c s VO in 0 CO in in o 0 CM CM O 9’ 0 0 0 0 © d H vO co in rl VO m £0 in 0 0 sr cm vn •Al- 0 9 « « ♦ rl vo © 0 O 0 σ co tn iS is m rl « in 0 0 CM CM cm tn Au 9 a * a » H vO 0 O O O O s IA S t> rl rl 07 lA 0 O rl CM CM O VJ « 9 • β » m MO 0 O O O 0 0 (Μ O bu X rl ς» FI Cm tt C Pi υ 0 H a: <5 O O w O -F< - VO tt1 -J rl IM tn •4 h rl m ω ^+9 rl r-l O> H S O m Π3 0\ G\ H σ\ σ\ Η. r-l ca 'ΜΗ Η σι rl 0' < Η Ον <Γ « rl ;η s <τ Η C O KO HA < t r- O', i rl rf I HA « Ok (o 4459 n cj <>\ ’L> 3) A TABLE X (Continued.) m m in CM (0 m 1 < • • HA • m *n o\ CM S • m • ’M H ri CM O H rf o σ» HA \.p ri • • • • m »n Cm Vi? in • CM H ri ΓΜ ri ri rl o ha co CM • • « ir\ HA cn CM vo in • CM H H CM ri ri cn CO CM in rl • * « Q m o CM co CM vo m * o CM H ri CM H ri ha CM ri cn ha •4 a a • • • in in m σι CM kO in • & CM ri ri CM ri ri rt MO * CM ri o HA ro CM * • • • m O HA Ok CM kO n a B CM H H CM H rt CM CM O • • • in o NA 0\ CM t- in « • CM rt rl CM rl rl ri kO O O • • in cn *4 O ha KA • • • « CM CM HA co •xj n- ri CM HA • t • 1 co in rt tn O HA CM a a * β . · CM CM HA tt) o c- N rt Ok Ok ch CM • • CM vO • KA Ok CM H * • ri * ri CM HA CO <1 ri ri s CO CM a • in rt tn o HA HA 0 a a a CM CM HA CO ω H <0 ts Ok * • in σ. CM ha o KA CM a a a • CM CM HA to k£) kO H o n HA O O * CM a a a a o o o Q ri ,M rn o -i o HA CM a « a a o o o O HA , n HA is 0k “i o HA CM • a a o o o o kO o CM rd Ok —i o KA CM o o C o kO CM uA nA CM o HA KA r3 a * O O O O kO un CM H Ok ri o KA CM a a • a o O O O kO in CM -4 HA ri O f-A HA • a a a O o o O CM CO •4' Ό m o O CM HA a a a a o Q o o kO vO HA s- CM o O CM HA • a a • o O Q O Ok Γ- HA -4 -4 Ο o. CM CM a a a a o O o O CM co 10 o o O CM < a a a a o o o o CO n < o CJ HA CM a a a a o O O O • Ok O CM ha in n a HA o HA « tn o HA CM a σ • CM CM HA tt) 4 rl H . } ii\ Cb hA kO Ό ,A IA -u o 1¾ if) .3 rt o Ό ha a\ o rj> co o m is o CM m rj • h in oa s cm m • rl o s· in Hmm • ri m o kO cj ir\ cm cm m • ri in o W ω C I i ha CM O if ι HAO o CM CM Ai‘ O (MO C > CJ f. } C' o o o o o O •A t J (j 4' -.4 rl CM r.; ·. ι d A.’ UtJ (U Su rj Ω -I ι.. <ή .:: r/j «ί iU X o O U4 r-« N σ: ι·ι S kO »4 HA O O m HA o’ O o O ΐΛ- C .r CM Ul o CM O ; I o «Η n U ΡΠ *0 O O O o H CC ί m ι t—j σ» H in kD co •4 ri kO ω JD - 13 ^4592 m in ni in m in m o CM E> β « Q □ H cn H CM • CM CM CM H H H m in m o CM o a 0 β a -g H cn H CM CM CM CM r-f r-f H m in m o CM o β a • r-t cn r-ί CM a CM CM CM r4 H H m tn m- o CM o a a β a H cn r*t CM ► CM CM CM H H r4 cn rn o cm m cm CO H in rn o o « © o vO vo m m o 0 0 O O H CU H in o bw OJ H m m o © r—j cm o O cn o CO H O O CM m tn CM co a O CM vo CO o tn m CD o CM VQ CJ ω ΓΜ 9.

TABLE X (Continued) cn co » ft) o O vo 0 m β o m to * cn b- 0 • cn rt CM is cn H o a VO β m o tn CO Γ- cn Θ • cn Η r-t CM IS 03 H o a VO o in o o tn CO a b- cn ts a cn H r-t CM Is 03 H o VO in o m co • IS cn is 03 H r-f CM IS - cn H O vO m co d o • o m is cn b- β 03 H r-t CM c- cn H O VO rn o co « a a tn IS cn b- e cn H H CM Is 03 rM o VO in o m co σ’ s 0 • 03 H H CM c- σ* ri tn cmo m re o cm η o •Η Η N i\ to < P< « 3 CM O CM CM CM I'M O O o o o o o o O o H 10 CM ω k ftl Jp k 4-S £< ΪΪ txi *4 O Vi Pl 5 H N bm Q o co in o co CM r-t O CM CM MO vo CM (ϋ H oooo VD VO H H • » OOOO o cn m CM r.n « co rn o co H oooo vo. •4· o H σι h H < a β oooo Ov o o o -r o o o tn o r^ rn » · o o o CM O fcu) γΊ k COO i£} co H « © in H O n CO O> H m H CM O m co cn H m ' H m r4 cm in • rn o m co h tn o in o tn vo m in o in tv) VD O VD H o m tn • CM VO o o m O H o tn • CM vir o N fee 0\ O'» H m H O', » i m ι ι cn H m » r. ο» H ifi H T3 Ci o O O H X Ci Acn cn UJ ia cO '.f CO tA \O (V CO J cn •d- • * CA e- ri 1-i m * 0 9 0 CO CM ri CJ r-t tv Uj CO H •d· CO • ri CD CV ri CO cn r~i A CV •d· ri cn cn • « cv co CV ri CM vO rl co -1 in in • CM r-i r-i 0\ O H in IA • • • CO in v0 m CM H r-i co ro VO .σ\ • « 9 CO in VO m • CM H ,H tA H CO H CO • • CO VO CV r-i H CM CO CM m - · « -+ co rl m • » ri CM ri r[ 0\ 0Ί C- • • » -+ ri in -+ , · • ri CM H ri m CM VO' H • • « m ro CM VO in • • ri CM H H CM J ! i ! .TABLE I (Continued) r*l ω o cD i.j O W 2: ri & -d tA . · h cn cv cv d· tA • * H cn cv cv tv O cv • · · CV ri ri ri · o NO CV . . > -d i-ι cv CV ri ri ri · O d· tn • · I-C O\ cv cv O CO • * A- cn ri ri CM 0 cv « • • -d- ri CM •d m CM ri ri ri • . 0 m ¢0 • 0 tA • N • • 0Λ CM n- cn H O VO m • IS « cn • r- 0 • tA • H ri CM A- cn tA CM O CM • ri cn H CM » CM cv CM pH H H UA CM • -+ * ri H m in in O CM • • • • -+ ri O\ r_i CM < · CM iM CM rH rl H ro σ H in CM • © P m CV O IA rno 0 CM tv CM CJ tv 0 O CM (V O 0 0 Ο O 0 O 0 O O •ri ι-l (V CM h n cv to itf k 22 •H i~ K W < 0. O-ί . - vi L> ro w cu H N X N rn rn co ri o K\ m O © © © CM -+ ·+ H Cj in rn • • • • O 0 0 © ΟΊ cn VO in CM MO 0 0 CM CM • • c, 9 0 0 O O in o\ CO in m m 0 p CM CM • • • • -0 0 O 0 O CO i<\ ri br-J O CM t~l · * · © © © © o r-i © in ri © vo m * rn CM *+ O CM r» » « • 0- © © O m <0 CM 0 CM CM • • • 0 O © ro in o\ m © ri H • • • 0 0 0 O n- m co 1> CM 0 CM ri * • • • 0 0 O O m CM VO CM 0 ri CM • • • • © © O O m co rn cn tn ri in o • • • • © O 0 © MO vo m ro Γη ri m • 4 • • © O d O -+ • ri m O\ ri ro H • • • • '© 0 O O n- ro 12» CM cn CM 0 CM * H 4 o- o* o’ G\ 0> in vO CM H CM ri ·· • · • » O O O O I iA trc O 0 * Η N O CV O Wj ο Γ-Ι <00 CO M) CM ifV «π « © ri VJ -+ m CM « O co O IA CO in ri ω <; O CO VO Oi in ri • O C; vo Vf> C•SJ H 0) GJ Γι O\ Ο O p r-j CU \i> 0 C* & G» I'-’ * O ri m t- O O ri V.» (0 o <3 in ri vo 0 ro *+ cv • CJ A- 0 0 cn in tA in • a> 0 N S IA rn 0 -) • ri 1- 0 cn 0 m t ♦ CM © CO cn IA co x 1 co -J· >0 ΑΓΗ CO <1 rt O CV ΑOO ri ΙΑ CV t'γη kr O ro H X σ o ri f i gm I r-i OJ -I t I Ov r-i m r-i 154 4 5i(5) ¢. ir\ cn t\I · · β · O 4 4 if) rt K\ CM r-l IO CM » fO ro * r-l rt r-l CO O CO cn S CO ts N svO s O CM CM S Ch o o CO O OX rt fO rt CM CM CM « ri cn o o · · σχ h ox rt CM CM rt O tO CM O CO Ox r-l VO H W CJ ri VO -4 • ΓΟ fO · rt rt cn s • tO fO · Η rt OX co * ro to « rt rt rt co tO rt rt ox β ro TABLE I (Continued) in is ¢- in s ti tn CM o o 4 « a ro tn in -1' r-t IO .-I tn ΛΙ r-l • rt rt m CO iS vo σ « a β o ro IS CM CM H ro rt ro CM r-f rt rt CD •i co v0 H v0 0 & o σ VO ro o CO o rt 6 * in CM CM CM rt VO r) rt • cM Scn vo to β Ui O rt#U »1 o •P cn O CD co » β β O CM to CD r-l rt 6 » tn CM CM rt vo cn r-i e vo m H rt » Q « β . -i H rt OX rt CM « « in CM CM CM rt tn (D rt • CM m o tn rt m 6 • o o « -i CM o CM CM rt • in CM m CM r-l rt H • o in t- to C- n- D « o CO •i CM o CM CM « in CM tn CM H OX H • o m CD tn b- β • « o cn CM Ox VO n- rt CM rl CM rt rt CM ro CM o to too o O CM Ο O CM CMC ο O •r-l rt CM CM -ri xd CM IV) eO wccuw^tehSBu Ο! « (M ο ο o © Ή 4 S β fO Cn H N B N —Γ ; vo t CM ϋ to CO » 1 IM »n %M o CM t V rt CM • • • i · t—i s © © o £ © to 'in σχ m VO fO l(\ CM o tM n4 rt CM β « • ♦ CM S O © O ί © t VO cn rt ro o •S m CJ C to cm rt CM • • β • rt S o o © o © ts -d* m ro rt o, 3; o CM O ro Cl rt r-l « o * CM £S o o O © O is in ro o CO ro O CM O to CM rt CM a 0 0 • CM S o O © © © VO m 4* tn ?O CM rt O CM o ?O CM rt CM » 6 e b β CM S- © © © © O VO ox m ro (s ro ox O CM O CM CM rt CM • « β β « to S o © O O o VO CM MO fO rt m in O CM o ro CM t-l CM * » • e • CM >· a o o © o s- ro vo fO CM IfX m O CM O ro CM O r-l • • « • • ro s © o o © o t- vo tS to co ro ro o CM o CM CM ro CM rt • « « » « rt IS O o o © o IS σχ σχ ro VO rt a CM- O CM IO CM CM • • » • • rt IS o o o o © ω oo in rt in m CM to o CM CM CM • « » • •4 s o © o O O rt CM rt m co in ro o CM CM rt -4* . 4 « • • » in S © o © o O to eo CM o fO rt o m IO rt vO to u « • '· vO o o o © © e-f o « ϋ V'J O T3 o o 3 rt t. Q <ς O O w O rib X C CO C5 e 1.437 1,439 1.437 1.483 1.450 1.434 1.484 1.433 1.433 1.433 1.434 1,465 1.436 - 16 Ό VA ιΠ σ* ο\ H 03 -4 σ O' tn 10 (j • • « • • CM Mi m m ' f. o 'MJ CA C'J CM • CM (Λ r-i CM r-i (M ri s -ί • 0 0 0 S MJ O m tn H co • • • M) • CM ?n « m CO H CM • r-i CM c tn σ» CM rH CM r-i r-i r-i O 0 0 o ri m o r-t co • « • • S- m vn • in CO o CM m CVJ 0 ca CM r-i CM r-i r-i <· ο ο ο 'Ji N\ 0 co CM • • 0 O N »n CM co •n • • 0 0 m CM • • 0 .O m m CM r-i ri MJ CJ CM c <3 ω η CA (V Ο\ 44502 cm ci u’ r-i S o m H 'Π fj •Η ο <α Η ω ► 3 ί? Η (h to r<υ o co in ω ιυ IP Vi · ιυ ρ r-i O 0 in S Ό H KO r-i » « • « vO • • s ca CM • CM Ch CM r-i r-4 H •4 r-i CO H m H IS 0 •4 * t • ·· CO • CO 0 rn • 0 CA CM H CM . r-i H m 00 ri CO tn r-i n • * « *4' • « ts O η · • CM ca H Cm H S' h MJ t- O in <0 0J s • • • O 0· • in CO H m • CA CM H CM r-i tn 00 CM co 0 m s m • • • * « H 0\ O vo CA CM tn • « r-i CM ri CM H CM m M) O M> VO VO m CM * • • • • m 0 S O CM tn • H CM CM CM r-i r-i CM O in M> CA CA CA • • CO ω • VO CA r4 CM • * CA CM r-i CM rH CM CM H VO CM H CA H • • • • O S O S CA CM tn H CM r-i CM r~i CM in m b- H r- tn tn is • « • • « m H 0 s 0 CM m « r-i CM CM CM H •4- S <1· m tn VO er VO » « • • Φ tT O co 0 tn bn • , r~i CQ CM CM H O CM CM f*,. in tn S r-i r4 < CA r~t • • r-i Cm CM CM b- r-i Γ* m (MO in no o o CM o o N cm o o •Η r I CM CM >ri ro CM hit ω s ί-M ii) ,q s; be: K 0 <0 00 2 L, β ΓΜ to 1? o CM O tfi 2 < O ,ν) •n CM O m 0 » 0 CM lf\ O CM co tn O CM 0 MJ • • « O 0 O tS co m V0 CM 0 *s4 * • • Q 0 O H O 0 s CM tn S ύ • c O m m lO m in • • 0 c lO r-j r-i r*i ω ω ο ΓΛ in r-l CM C m tA < ο ο ο o a H CO NJ -4 m CM a m m 0 0 0 0 a) m m co s cm o tn tn o o o o Η tn m r-i • Φ r-i Cl r-i m in VD O ’-Ω vO O CM η vo O MJ t'- ω H k O •4 VO iv r-i rH ΚΛ S- CM rJ O cm o tn jn m .....IS VO O O 0 0 ts CO tn CM CA CM O tn tn • • • • ω a cm < o „4VO 0 O Q σ 0 \D CO tn •4 s O CM 0 «4 m rH S « » • • • m vo O Q O 0 O 0 ω in 0 tn CM 0 » » • Q 0 0 0 to vo q i~i -u • in vo 0 u) m io nJ ο n cm e· cm tn (-i CO t-f Un Pl C o K X in r-t ca r-i m m o in H ω o\ H σ\ H m H m ri VO ca •4 « H H 0Ί H m -i* rH Ch O H CO o H o rf n. r-f co tn o σχ to rt r-l to o TO O CO --» • . · « ox co o to . rt r-f CM rt CM rt v- in vo o n- o W w vo m CM *- - 0) o to CM « b & CM ,S to co σ m σ σ o r-l to ts co to O rt CM • b in rt o CM s σχ CM ♦ β CM rt CM to in to co rt ox rt O - CM o VO o co σχ -co vo β & « β - C3 G3 - ox o O ts σχ CM rt rt CM rt CM PO in 04 < rt tn cm tn -i <0 ·© o OX cs cn . is « e «. ·; rt TO OX • o to σί CM β o .» • CM rt CM ϋ- f£> - CM co TABLE I (Continued) in o H w I? » ft! O o „ σ o in ώ co io o M3 o ·- e « LO & rt cn cm rt cm io is cn rt to ω in © is cn cm rt CM rt CM ri? in CM ω CM ro CM S CM co tn O m tn o Ox OX ox - β « a o- · - co CO « vO ox rt . Q • σ CM rt CM W rf CM -- s Ox CM 0 tn to cn σ β b » 00 : ¢0 VO OX .rt w CM rt CM - . .. H : ftl C~ ft! O in VO Ox Ox • σ • . CO o vo cn rt CM Ox CM rt CM rl CM CM O m to OX Ox « 9 β - . co 0- v0 OX rt CM e cn CM rt CM rt CM CM 0 m vo Ox σχ * « « ¥ m tx> OX. rt • CM ox CM rt CM rt . cm rt VO O: V0 to rt • ·- » » » rt o ts o CM to rt CM CM CM rt σχ co cn co Ox. ω s vO ro ux rt CM O VO m • • a Ο- o o © Ο s M3 ro VO CM O ro ro β * » • O © o © s OX to m OX CM o m to • O b a o o © o ts vo o OX ox CM © ro o β 0 a © o © © s vO ro ox 0x CM σ .tf- to a « « • © © o o s- CM KX ox co CM © TO CM « • * a O © © o s Os ro to CM CM σ <3· ro • « O © o © in to ro o S- CM o vo to « « - e « O- © o o • ro rt to co rt CM. o ro TO . · β • ft O o o o co ts to ox rt rt o CM to a b * o o o © co o to o CM CM o m ro 0 • © © © o s co co η CM © m to - ® » 4 • O_ © © © co CO to o CM o «X « • & » © o o o to o CM tn S'* rt in · o < rt m • CM Mj m m io « r-l to o m co to VO to CM <3 CM O VO «- CM \D © O CM rt rt VD S· -O rif σ* to tn σχ o IfX m a ox m _-4- s * in to . rt O co vo o rif CO to o rt rit.vG rt gUI vvy wo m no o tj wo o ni mo - _ nJ w ·,-! » - w tin u s’ CM CM Ci σ f3 o Q OO CO ω' XI rt W Si C o V3 fp P4 N JS ts? 16 O CMC bO 0 rt - O U CQ H Cm C Γΰ Ω O Q C H o ic tn CM f-l CM CM rH H CM ft VO O CO m · . · * rf Ν ·4 0) m oj p-i vo o m in • H <\| 4 qv m cu μ SV ft CM fi Φ (\i ω CM o rt ft CM b- VO a • • • • ω o tn tn m CM ♦ ft tn CM H r-t m co in co in b· co 4«J$92 i~i CM o 1« \ o a o rp tn o ft CM tn I b λ O iH o o i.n CO CM CM tn Ch -d· O t: \ CM o m CM -e 0i , a * • » a CM VO rt o o o O o T5 tn OOOO H o co m in o r-t a V • a • CM • o fi tn fi H Ch K\ CM fi fi η © CM CM CM O Oh a a a a -il © fi o Kh tn un ' rn « « ft ft tn CM fi fi ri GO r-i ri co OOOO i t t • n S : cm c in t o o o vo a m m · · · ο η ω<τ 0\ m CM - rH CM fi ω CM co in ω 'Λ VO o tn vo b· cn ff\ o · t • cm cm CM η CM Ώ in CM t> m ο h • b- vo o O' o in rn © < O', i * Ό vQ . ft I O Mx m e.g : vr-ί VO ; fl TABLE I (Continued) v0 H in H H ft H CM H H H ft ft O H ft (0 V) · <ϋ o r+S O o in CM CM co vo © a a O ό rn m in CM a a r-t tn CM H fi ri •4’ CM O CO VO a a · a o -4· tn in r-i lh S3! rt tn H Ch O m -4· CM VO VO 03 H in a • o o tn ω tn r-t tn CM rl H on co m CM tn H tn vO CM m a a a • m 00 o tn cn CM ft CM r-t r-t rn m r-l < m ω tn VO a a a • . m ω o tn 03 CM H CM η co co CO r-t r-l CM cn o CM 0) • β a • tn vo Ov Cm ω CM ri H fi CM CM CO ft co O m VO O o a • a b cn tn o’ CM H H ft m * fl tn no m *nο o O •H in $ CMC Ο N rl CM CM < Pa 10 U tn cm co 0» CM CO CM CO in m co tn co vo ri rt CM OOOO w Μ) W k <0 tA E u CO CQ S Ν Ο O RS ft tn crco CM Ν (N o ooo •H k IU C ω ι co rn κ i cm o in CM bm /μ I · a a a a CO vO j O © o o σ co in I m tn o CM in ί o tn tn CM o\ a a a I rn vo o o o o O co m VO tn tn co O\ in CM O tn tn r-t Oh a o ό ό ό ό VD ω 4· o m b. rl O tn o CM tn CM Ch o ό d ό ό m vo !> ?n m tn \0 b- CM o CM H a a * a a σν vo o o o o o b- CM fh rn tn ω O b- tv o m tn ^J· © ft a • • • -, f! vO o o o o o b- 0 m m *4* VO ;n m CM o -4 tn 0 ft Ox • • • a a CM in o o o o o b- CM m t- ft C'x o CM © tn 4 co a a a a a H vo o o o o o E-i o U, O CM o •d « o Wi 0 fl P R ϋ H o O rt O rVM W TABLE X (Continued) CD CM CM ch S .--. Κ- rt ch m. rd ω CM m m » e c o ts -4 - o o H -4 tn 6 Ch m CM rd trt CM (S in kO co tn tn rt co n- • « 6 t> b- co [> CM CM -4 . - , e e σν m CM rd Λ0 KO _ CM IS CD O in t> CO CO - -- cn in b . e> ό G\ cn c- tn o rt cm % . -« Ch rn cm rt rt 0\ CM d CO o in. rt co in in - β • β o CO tn o • rd tM di- , CM σν m CM rt rt CM is d tt tt » Oi o rl25 a m cm o in mo o o moo cm cm ο ο o rt rd - CM CM -rl Ci CV W> itf - 2fc CM c- tn cn cn m sr is CM o tn CM m in rd 6 & 6 • -4 kO o o t- o o o Es CM rn b- tn cD N CM o CM m rd df CM • • a e o rt CD o o o o o -4 ¢- tn o o in tn cD CM o rt m rn CM CM • * 6' • rd CD o © o © o ώ ω tn rt tn rt σ 9 CM o tn tn rt m « β rd CD O o o o © o CMO feo σ rt Ch T) a έ Π ΰ O o H < o u W o rvi CD a m ri rn ri m ro o m m O in « Π - 20 44502 ιη Η rl • -+ vO O o H CO co CM co VO in in cm rH rH • • rH m CM r-i in CM a ό rl A rH VO in • m • in tn rH d CM ro o CM • CM σ ri CM rH rH rH ·+ rH « ο • co * 03 • o ro ro tn is σ\ 30 ro CM CM « 4 rH m CM A o m ΙΑ Ο Ch νθ CA s s ~+ tn · Η CJ η Η ri s « OV σ» ro οϊ ts CM m CM Η νθ -.0 CM tA O s m o « • 4 o o o lA IA cn CM O vo CM • • • » O O o o CM IS tA tA w • o d IA o CJ d o •Ο fn co ro o in cm ό ό ό CM m o CM » O ro CM ro -+ O .-I • IP, VO o ro CM o • o -+ o tn ro ο ω cv Η <0 ro Ht in ro rl ,v0 m • 4 « ts • !cm tn Α- 03 i o H d cn tn tn • -+ · o ΙΑ ro n ·+ ?n ri CM H H rH cn rH o d d ¢5 ! a w ro H « 03 * cn 4 co • cn m ro rl ro o H tn O\ CM CM CM rH rH 4 o CM Ο ιη m CM V\r in rt σr-1 in 4 • rH -+ CM •n e H ro r-5 m H Q> Ο d •Η Ρ c: ο υ rH • rH • CM 4 Al A 4 H ro in CM σν ro ro S •d Hf m • 4 • • H CM rH rH rH tn CO H H Μ »4 Η H • (A • ro • Ch • A Al CO O O Hf H • • • ri tA ri CM lA IA tA co IA • Α- cn lA 4' ri • CM co vo CJ tA 03 ro ΠΟ • σι -d 4 • rl At A rH rH tn © rH rH Η ιη Η Ο ΝΛ Η CO CM H ifl in rH » a «V. 4*1 ro S A H tn • 4 • 4 * ri m CO tn ro tn • rH CM rH rl rl tA o m o ro 4 β 4 tA ri co A • CM ro H • • 4 4 cn in rH CM IA m CM A Al ro β co 4 s 4 in m V -+ tn A ro o VD β CM ri CM ri ri H rH tn a\ ro 4 tn • rH rH m in in in s Oi rH S o 4 « rH CM rH rl H rl cn ov CM Q in O CMC mo Ο 'M o o o o CM O O CO ru o ox' o •H rl CM CM ·.( 1:0 re Ih (ti J □ ·Η k CH © W < fXi in »-i *--S S5 ro CO ro £ M fcH N N o co ! A ro s CM O CM » . • 4 o o o © ro tA 03 o CM O -d rn 4 « • * o o o o tn A tA A cn m O -d tn • • • » o O o σ 03 co tA -a· 30 C3I O 3- Al V • • • o o o o o 03 Al tA A •d o H3· Al 4 o o O O rH 30 A ro ro m O -+ m • « « 4 o O o o tn in IA in tn tn -d CM • o O • o 4 • o o o tn m ro ro tn tn -+ CM • o 4 4 o A o o ΡΊ + Η Ο S νθ '0 Ο Ον Ο νθ • VO νθ D s ο in co co • Η VO Ο ri A « -+ CM O ro ro O A O © « VO s H tn ro co o o CM s o O Cd A o O σν s CM « o CM ro m o m in CM d H vO Ch Cm n u TJ o 0 ri (•H o X ro in H -+ CM in r-i S H in • ri ro CM in rH CM m H rl r-f in CM cm m H tn CM in r-l 44502 TABLE I (Continued) CO S vO VO s s tn m e « « » vO 0 vO tn CM tn in 0 in O a) O rl β rl tn CM 0 tn CM -d O K H CM CM CM r| vo rl * ο 9 9 • * tn s . 0 O 0 0 O O s in m CM s* vo ro i-t m in 9 -* CM 0 OV in σι O'» IM Q Q m β O\ 6 tn CM • rl rl 0 CM ro rl ό rl co CM CM rl rl S' rl • • » * . CM s 0 0 0 O 0 CO CO m VO Ov cn tn tn rl tn vo rl tn CM cn s S' m in -g CM ro 0 un « tn d o o- 9 9 • CM 0 CM tn 0 VO rl ω tn rl CM tn S’ CM b- 0 • 0 O d 0 0 CM vo 0 σ 0 r-ί s O in O co o 0 e CM 0 tn tn tn cn s tn 0 in co s ov CM 0 VO β CM 0 ts s* w rl VO rl co CM rl rl . rl CM rl rl 0 0 « o ό 0 6 O CM 0 rl VO s O rl CM m s VO VO S* GV & β S' CM ι?} CO rl £ 0 S’ CM IS in co ό r-l 0 tn m O o\ r| CM rl rl H H • * rn to O 0 0 0 O in ts H in m H CO cM 0 0 9 ts S b- XV CM in CM 0 s- « S' S d to 4 • CM 0 VO tn S CM H H σν CM rl CM rl CM ts 0 0 a • 9 s vO 0 0 0 0 O 0 VO S' VO O CM s CM S' n- tn S' tn ts 0 0 • 0 0 rl « i-t tn s 0 O m cn S’ s ft ’A tn 0 s- tn •l. CM vo rl H CM rl rl in tn rl . 9 • a 9 H vo 0 0 0 O O s rl CO O in VO S σν CM in CO CD VO 0 • β a s CM co O m m S’ VO O O S tn tn tn rl s « 4 • tn 0 s* tn rl vo rl rt tn CM rl tn tn CM CO • a • 9 tn vo • 0 0 O O O in in tn ts in 9 ο- * O CM tn cn tn tn σν rl 0 s· ro νΟ tn CM 0 CM rl r-l 0 rl H rn CM d CM d . 9 • • 0 s s o_ 0 0 0 O H tn vo co CD »n Ch 0 s vo CM O CM m tn rl r| s . ω 9 H 0 in 0 s- S in rl vo e O 4 • 9 • 9 CD co H H rl CM rl Ov CM O 0 0 o 0 rl vo co m S O O CM ov m in «* 0 • 0 VO 0 tn ro ω m irv in s· . s VO CO tn • VO CM O m s Ov tt CD rl CO CM rl rl r| CM rl β • 9 • 0 rl un O 0 0 0 0 tn tn Ov rl O CM vo CM 0 « 9 s- b tn ov CM S' tn vo ·.·*· 0 S' s co S’ rl β • OV CM 0 3F CM ‘O S C3 rl H CM rl rl rl rl ιΛ 03 • • • • 0 CM liV O o 0 0 O O σ» tn co rl tn CM CM rl 0 0 co tn • β vo in CM OV CM 0 S’ in co 0 O rl CM 0 -i CM VO is •ΑΓ rl rl CM CM d rl rl rl 9 • . • 9 CM VO O 0 O O O W ' CO » rf O in ti rl S CM O tn tno 0 CM CM O tt 0 OSO (MO 0 CM CM O O O O O 0 O O O O (VJ 0 Ό a 0 1 > -rl H CM CM -ri rf CM uo rf rf ♦rl Sm VI u no 3 H tt Q 0 H 3 i CO tt m ϋ bi £ O co W tt C-i ΙΜ IE N S U υ « O un a: 1.523 1.521 1.4S2 1.505 1.402 *’525 1.520 1.450 - 22 4 4 592 MO MO rt MO ri «4* MO rt ns MO rt cm mO ri ri in c- rl ri •4 t 9 • 9 • MO b mO os co 1 m CM CM ri Φ • • • • rt NS CM ri • NS US CM b j O sm m cn o cm o -4 -4 ό ο ό ό MO n- s ri in o • 9 9 9 9 ri NS CM NS CO NS MO NS 9 9 • ri CM ri ri ri m cc ri co CM o ω ri us 9 • 9 • •4* CO NS b b 9 CM H CM ri ri ri Q\ NS ri m •4 cn CM us a a • a b Ch US ts CO 4· •4 a 9 cm os rt CM ri rt ri Os ri 9 o NS -4 MO MO • 9 9 « CD in CM MO NS b b •b 9 • ri CM ri ri OJ OS in CO nm -4 O Hi • ri uS O r-t H t I US OS O CM o in US o 4 CM 9 9 9 o o o o ο moo o in in o in o O US m co mo m US CO ύ j ό π m IS us m NS OS ’ us O NS o us cm m rt b • o ό ό ό ό CM mO ri CM I rt TABLE I (Continued) ri MO rt O ri Os m rt ri b in ri MO in ri in in H 4· its V) · Vi o fj «—« rt 0 o ri NS •4 o 9 9 9 rt os u OS CM MO Os OS > · o ri CM ri ri CM rt CM b o s •4 rt 4 9 9 9 a o CM m MO MO o NS 9 9 • CM rt CM rt NS. CO CM CO o 4 US cn CO • 9 9 • M3 o· o NS -4 b Os c- • • 9 9 rt CM ri rt m US m co rt in CM CO CM a « 9 9 a ri 4 4 s CM Os NS « rt CM rt rt ri NS d noon • · · · rn mo os -4 in · ri CM rt ri rt rl 4 b O • « ♦ » b o ri NS ri H NS b Ch CM b o CM ri CM η b m m · · · * vO MO o OS CM ri CM NS NS Os ω Q Ch CM NS co co rt co co CO ω NS » . ns cn co m ri CM to o in mo in no o nj ο C? W «O ?: -H rt « rtlTl (J CM v ui 1 y id O O o o O O (tf ίκ nJ .n •H O w W ΓΜ N OS ~ MO NS g MO CM O NS ο ό O e m o m m m in o IS in m η- σ ν ο 4 4 <5 ο* ό ό Λ Ο CM W -4' φ rt tD irt CO ο to ft! t~ Λ Η ω CM O rt Ό Ο Μ f-j ίΓ. Νί 4 b b NS σ CM NS US CM O MO NS MO o MO • a 9 9 a NS MO O •o o © o NS MO in NS co VO NS it o CM 0 NS CM b ri rt 9 • 9 9 ri MO o O o o d b ri US NS 4 VO CO o CM O 4 CM US 4 Ox 9 a 9 9 9 CM US o o o o O MO NS co NS in CM O o CM O m in 4 CM rl a • _· 9 ri MJ O o o o o 4 CM os NS ri NS '-0 o NS O US us to ω vO a a • 9 9 ri M£J o o o o o b o fM O Tl Q O t.o 3 rl Fl a O rt U U o 4f* X TABLE X (Continued) tn brt CM CM ro rt σ 4 a D • co • ox S CM CM • cc rt r-i CM rt ft! rt 1S rt nt brt LO tn CM to σ • o • ft co LO rt OX CM co CM rt rt rt CM bσ KO rt r-l brt ro ES VO to m » o a • 0 M3 v(3 o M3 σ CM rt CM rt KO ft is o s * rt rt in co OX rt ox rt i. vo OX • B « 0 rt * rt rt rt KX Ch tn rt ft) rt tn OX VO rt o VO rt S b- tn rt CM rt -ί- CM m a « • • ro ο ro « tO co o iO ft ft • σ CM rt CM rt rt ro CO CO VD rt rt in ft rt 0 o 6 b- o rt rt ox rt CM • •4 • CM CM ft! H o rt rt s v£> rt ro σ Ox tn rt tn o rt ro a rt tn rt rt ft) tS S to ox • a o s ro co Ui o W o rd 1m ro rt CM O in tno O CM CM CM o CM O O w NO o o o o o o O O Ο rt CM ft! -ri CM no ro p (0 ,o •ri h Π Ch fQ μ) X o to CQ ff IM 34 Ν in ox tn ro o CM o rt -Ί » ft O o o o ft! O in -Ί to CM o in IO O ό ό δ m in tn o rt CM o ro • • ft a o o 0 O b- CM tn oo CO ro o rt CM • • 9 a o o o o b~ •d- in to vo ft! o tn ro ft ft • • o o o o b- rt tn m CO CM o CM rt a ft • • O o o o vo -Ί- to σχ CM Ο rt CM a 0 O o o o O CM O ω -ί < ο rt Ο Ρ Pl in rt m co IO o οχ ω δίη σχ co rt • rt CM ox rt • CM O CO ts lO Ol • rt O rt LA VO vo « ro o 690 650 630 640 635 650 600 tu Ω Ο Ο ο Η X - 24 44502 The following Table II lists a series of photochromic glass compositions according to the invention which can be chemically toughened by ion exchange as mentioned above wi-ch the compressive stress in pounds per square inch and depth of penetration in microns achieved when the ion exchange is carried out by immersion for 16 hours in a molten KNO, P bath at 470°C, as well as the photochromic properties of the toughened glasses. In the case of glasses 174, 175 and 178, the exchange is of potassium ions for sodium ions. In glass 176.potassium ions are exchanged for sodium and lithium ions. In glasses 1?7 and 179, potassium ions are exchanged for lithium ions. It can be seen that the chemical toughening process does not affect the photochromic properties, e.g. by comparing the properties of glass 174 with the very similar glass 71 in Table I. - 25 44502 VO . > w to 0 ctf O H <3 o TABLE in tn cm tn o . . o m tn s o cn > rl (M W t-f CO 0\ CM CD r-f O H co VO GA 0 ϋ « t-f tn f> CM in 0) Γ- H ft o β • • rl nj Η H vo σ\ CM t- rf ri VO o • « O tn cn CO tn CM CM rf a ft • e rf m CM rf m CO CM c- o H b- tn tn « © » 03 CO CA o CM CM H O' • a • rf tn CM H H r-i in w CO co t- co m in • a o in CO tn o in CM vo • • • H tn H O' vo H tn in r-ί tn r-i in 6 A β • O’ CM o CM CM r4 • CM tn CM H H r-f CM o m mo o O CM Ο O CM CM o O o σ o -P •ri H i\i CM H CO CM to (0 nj 2c < PU « H a >4 o co « w n; O O i-ι -_H m n- m o co cm O in CM * c 0 o o o o CM O ό ό ntn cm in “ m tn s o in ra -i cm o tn m & ό ό ό tm tn in CM O CM CM • · 0 · o o o o r-i 3 in m m o CM CM • • 0 • o o o o O CM O W3 3 H U, O 03) o o G\ m tn tn vo o vo m tn in m ¢5 σ 0*0 <3' VO H (\J o o to tn vo CM b* O o tn cm σ*\ H o o O’ o- h c<- co .

O* CM o O' o o O' h m CM CO Ο O in tn H CD CM CM o o H o- m cm in o o* .¾. ΰ o »K -P - 26 44592 The compositions listed in the Tables can be wade up in the following manner. The batch is molted under oxidising or neutral conditions at a temperature in the range 1200° to 16OO°C, and after cooling is annealed at a temperature between 450° and 65O°C. A final heat treatment may subsequently be effected at between 20° and 100°C above the annealing point for a period of 10 to 60 minutes. The optimum heat treatment temperature range for a particular glass may be determined by a gradient furnace technique. In some cases, it may be necessary to support the glass during heat treatment to avoid sagging.

The batches can be made up from conventional glassmaking raw materials, such as carbonates, meta-or ortho phosphates, nitrates and oxides. The silver and halide components may be added to the batches in the form of finely-ground silver salts and sodium or potassium halides, respectively.

Precautions are required during melting to minimise volatilisation losses of batch components. Up to 60% by weight of the halide components and 30;S by weight of the silver may be lost in this way and the necessary allowances are required during batch preparation.

The glasses disclosed above have a useful combination of photochromic effect, measured as induced optical density, with speed of response to exposure to, or removal of, actinic radiation. Although in some glasses it will be seen that the induced optical density is not high, the speed of response in those glasses is particularly rapid.

The glasses can be used for ophthalmic purposes and for other applications where temporary protection from actinic radiation z such as sunlight is required with a return to normal transmission when the actinic radiation is absent. They may thus be used for glazing in buildings or vehicles in some circuiisti inces. ~ 27 44592 The production of photochromic prjportios in a glass is associated with the formal ic1·/ of silver halt da crystals in the glass matrix in a form in which they are sensitive to actinic radiation» Hence the glass maker is not only faced v/ith the problem of choosing a glass composition which can be melted and formed satisfactorily in a particular commercial process, but also the problem of achieving this in a glass in v/hich silver halide crystals v/ill be produced in radiation-sensitive form, so as to give the glass satisfactory photochromic properties.

Many suggestions have been made to explain the behaviour of the silver halide crystals in the glass matrix, and British Patent Specification No. 1,428,880 even suggests that in some . circumstances and v/ith certain phosphate glass compositions, the silver halide may be present in the glass matrix in non-crystalline segregation phases.

In view of the large number of components it is possible to incorporate in a glass composition, it is in practice Impossible to investigate fully all the permutations and dombinations of even a selected area of glass compositions such as is defined in a patent application for a simple glass composition not involving the behaviour of further additives. The problem is increased in the case of compositions where a further physical effect is produced by the addition ofother additives, such as those of the present invention. We have made a large number of glasses in the course of our investigation of the composition area claimed in this application. In the examples selected from this work and listed in ths Tables above to illustrate our invention, we have in particular illustrated the wide variation in composition which io possible within. tha defined area in terms of the major glass ^^·:.άΏ2 cerpoucrfu AlgO^, and P Ac indicated above, we prefer to operate v/ith Αϊ-,ΰ-, as the major component. Examples are included to illustrate this for varying relationships of to PpO^, i.e. from greater than P/d to equivalent to ?2°5’ and 011 wkere PgO^ greater than We have also provided examples to indicate that it is feasible to make suitable glasses v/ith either or PgO^ as the major component. The examples further illustrate the possible variations within these ranges, i.e. BgOj> ^IpOj> P2°5 and ®2°3 P20^> Λ120,> and P20^> B20~> AlgOj.

The level of SiO^ in the composition has little or no effect on the photochromic properties of the glass but does enable one to adjust the forming properties of the glass, and can, for example, be important in achieving a glass which can be easily toughened by chemical means. Hence the adjustment of silica level to accommodate changes in the other major components (Al^Cu, PgO^, is a matter of applying the ordinary skill of the glassmaker, and the knowledge of the known effects on a glass composition of such changes.

Examples are provided in Table I το exemplify the limits cf the permissible ranges fcr the major components, 4 51) <2 but in addiLion examples of gls;:: os in which inf; m?.jcr components era not at the limits of rangoa are included to help to guide the practical glass maker to those areas where the most useful glasses can he obtained and to indicate that a large number of glasses exist and have been tested to identify and prove the valuable compositional area which is the basis of this invention. The Examples are in no way intended to establish discrete areas within our bread disclosure in which the advantages of our invention are obtained but to 'demonstrate that glass compositions may be selected over the total area with a particular preference for selecting glasses in v/hich AlgO^ is the major component.

The selection of a suitable base glass composition must also be accompanied by selection of appropriate quantities of the photochroraic additives, Ag^O, CuO, Cl and Br. The possibility of varying the quantities of these additives in the same base composition is demonstrated in. e.g. Example 43 to 49. Other variations in this composition are shown in Examples 7, 8, 9, 57 and 58. It will he seen that, in general, with an increase in the level of AggO there is an increase in induced optical density. It is therefore important in selecting a suitable base glass composition also to experiment with and adjust the level of photochroraic additives to give a desired induced optical density in any particular glass.

As mentioned above, a final heat treatment may be effected, and there may be with some compositions a need to investigate the effect of changes in both the time and temperature of the heat treatment to cause the separation of silver halide crystals in the glass matrix so as to achieve an optimum performance from the particular glass.

This can be conveniently done using a sample rod of the glass - 30 44593 oust in & gradient furnace. Examples showing c- variation in heat -treatment temperature with some variation in photochromic additives while maintaining almost the same base glass composition include Examples 12, 50 to 56, 59 to 61, and 72 to ,74.

Further adjustments may be needed in the level of photochromic additives and the conditions for heat treatment if a composition is further adjusted by composition changes to give a desired refractive index such as 1.522. The adjustment of a glass to the standard ophthalmic refractive index of 1.523 + 0.001 can be seen to be feasible with the glasses of the present invention. The majority of our Examples in Table I where the index is or has been corrected to 1.523 + 0.001 are in.the area where Al^O^ is the major component in the composition, as this is the area where the combination of properties achieved has been found most advantageous for commercial scale production of ophthalmic glasses, but it will be seen that Example 173 also has such a refractive index in a glass composition in which is the major component.

Claims (18)

CLAIMS:

1. A photochromic alumino-phosphafce glass having silver halide crystals dispersed throughout the glass, the glass comprising as non-photochromic components in weight . percentages: Sio 2 - 8.5 to 25% 13 to 36.5% _ ? 2°5 7-5 to 33.5% -- B 2°3 .7 to 2S% SgO 7 to 20.5% where SgO represents one or more o £ NagO, KgO and the maximum content of Li gO being 5%; the amount ι not less than .155 when the BgOgcontent is less than 3%; and, as photochromies.components, expressed as weight percentages over and above the 100% total of all the non-photochromic components of the glass: silver, expressed as AggO hot less than 0.05% Cl+Br 0.20 to 2.0%.

2. A photochromic glass according to Claim 1, wherein the largest constituent is AlgOg which is present in an amount not less than 22 weights, while the content of PgOg does hot exceed .25» 5 weight % and the content of BgOg does -. not exceed 24.5 weight S.

3. A photochromic glass according to Claim 1, wherein the.largest constituent is Bg°3 whicl1 is present In an amount not, less than 25 weight %, not exceed ZQ weight % and 20 weight %. . ' . while the content of AlgO, does the content of PgOg does not exceed - 32 =1 4 5 a 2

4. A photochromic glass according to Claim 1, wherein the largest constituent is P 2 °5 w hich is present in an amount not less than 21.5 weight %, while the content of Al 2 O 2 does not exceed 26 weight % and the content of BjO^ ^ oes not exceed 17.5 weight %.

5. A photochromic glass according to any one of the preceding claims, wherein the silver content of the glass is not less than 0.06% by weight over and above the 100% total of all the non-photochromic components of the glass.

6. A photochromic glass according to any one of the preceding claims,further comprising as non-photochromic components from 1 to 21% by weight R'O, where R'O represents at least one of MgO, CaO, SrO and BaO, within the following individual limits: MgO 0 to 4% CaO 0 to 6.5% SrO 0 to 10% BaO 0 to 21%

7. A photochromic glass according to any one of the preceding claims, wherein R 2 0 represents a mixture of K 2 0 with Na 2 0 and/or Li 2 0, neither of Na.,0 or Li 2 0 exceeding 5% by weight.

8. A photochromic glass according to any one of Claims 1 to 6, wherein R 2 0 is K 2 0 alone.

9. A glass according to any one of Claims 1 to 6, wherein R 2 O is Na 2 0 alone, in an amount not exceeding 14% by weight.

10. A photochromic glass according to any one of the preceding claims further comprising TiO 2 in an amount of up to 6% by weight. j 4 5 ίί ά

11. A photochromic glass according to Claim 10, wherein the TiO 2 'content does not exceed 3% by weight.

12. A photochromic glass according to any one of the preceding claims, further comprising ZrO 2 in an amount S of up to 10% by weight.

13. A photochromic glass according to claim 12, wherein the SrO 2 content does not exceed 7% by weight.

14. . A photochromic glass according to any one of the preceding claims, further comprising PbO in. an amount of up to 8% by Weight. . 13. .. A photochromic glass according to any one of the preceding claims, comprising as photochromic components in weight percentages expressed as quantities over and - above the 100% total of all- the non-photochromic componentsi

15. Ag 2 O 0.06 to 0.60% Cuo 0.005 to 1.0% Cl 0 to 1.0% -- Br 0.08 to 1.0%

16. A photochromic alumino-phosphate glass, substantially 2q as hereinbefore described and in accordance with any one of the foregoing Examples 1 to 82.

17. A photochromic alumino-phosphate glass, substantially as hereinbefore described and in accordance with any one of . the foregoing Examples 83 to. 127.. 25

18. A photochromic alumino-phosphate glass, substantially as hereinbefore described and in accordance with any one of the foregoing Examples 128 to 179.