Fluoride glass compositions based on actinides or yttrium

Abstract

Fluoroglasses, their preparation and intermediate products obtained. These glasses are characterized by containing as the forming element at least about 10% by moles of a metal fluoride or mixture of metal fluorides of the formula MF.sub.n, n being a number equal to 3 or 4, M representing a 5f transition metal when n=4 (fluoride MF.sub.4) and a 4f transition metal or yttrium when n=3 (fluoride MF.sub.3), it being understood that said glasses are free of hydrofluoric acid as the forming element.

Description

This invention has as its object new fluoroglasses based on actinides or yttrium.

It is known that certain chemical compounds, alone or associated with other compounds, make formation of glasses possible.

Development of infrared applications, particularly those using atmospheric windows around 5 microns and 9-10 microns, has led to the search for new transparent materials in these regions, and in particular, for glasses, considering the ease of shaping and preparing them.

Materials traditionally used in these infrared ranges are monocrystalline germanium and chalcogenide glasses derived particularly from sulfur, selenium or arsenic. However, these materials lose their transparency with temperature or are sensitive to the oxygen in the air.

In recent years, use of certain fluoroglasses, particularly glasses with a beryllium fluoride base, have been proposed. However, these glasses are costly, toxic, and their transparency in the infrared range is limited.

Glasses with a base of certain fluorides such as ZrF.sub.4, HfF.sub.4, AlF.sub.3 or BaPO.sub.3 F have also been proposed.

Glasses derived from ZrF.sub.4 or HfF.sub.4 are relatively easy to prepare and use. However, the transparency of these glasses goes only to about 7 microns.

Finally, it should be noted that the formation of glasses with a base of metal fluorides and hydrofluoric acid has been mentioned in the literature. However, it was found that the resulting products were not glasses.

This invention has as its object new fluoroglasses with a base of fluorides of actinides and/or lanthanides. These new glasses offer the advantage of having a notable transparency up to 12 microns.

The fluoroglasses of the invention can be prepared at relatively low temperatures.

Another advantage of the new fluoroglasses of the invention resides in the possibility of including therein fluorides of 3d or 4d transition elements.

These characteristics of fluoroglasses of the invention give them advantageous properties, making possible their use particularly in the optical range using infrared. Their index of refraction and their dispersion of indices are different from those of known fluoroglasses.

This invention has as its object new fluoroglasses characterized by containing as the forming element at least about 10% by moles of a metal fluoride or mixture of metal fluorides of the formula MF.sub.n, n being a number equal to 3 or 4, M being a 5f transition metal when n=4 and a 4f transition metal or yttrium when n=3, it being understood that said glasses are free of hydrofluoric acid as the forming element.

Metal fluorides MF.sub.n are therefore those of formula MF.sub.4, M being then a metal selected from the group of 5f transition metals (actinides), and those of the formula MF.sub.3, M then being a 4f transition metal (lanthanides) or yttrium.

Of the actinides, thorium and uranium are mentioned in particular.

Of the fluoroglasses of the invention there can be mentioned particularly:

1. those that contain up to 50% by moles of fluoride MF.sub.4, and, further, in a proportion that can go up to 60% by moles, at least a fluoride of formula MtF.sub.2, Mt being a metal selected from zinc and manganese. These glasses, for example, contain 35 to 60% by moles of fluoride MtF.sub.2.

These fluoroglasses can further contain as the lattice modifying element, generally in a proportion that can amount to 30% by moles, at least a fluoride of the formula M.sub.II F.sub.2, M.sub.II being a bivalent metal of great ionic radius, greater than 1 .ANG., selected, for example, from the group consisting of barium, strontium and lead.

These glasses, in particular, are those that are free of fluoride MF.sub.3 or which contain no more of it than 5% by moles.

Of the glasses of this category, there will be cited particularly those that contain, by moles, 20 to 50% fluoride MF.sub.4, 35 to 60% fluoride MtF.sub.2 and 5 to 30% fluoride M.sub.II F.sub.2.

2. those that contain as forming elements up to 55% by moles of fluoride MF.sub.3 and up to 65% by moles of fluoride MtF.sub.2, Mt being a metal selected from zinc and manganese.

Of these glasses there can be cited in particular those that further contain, as the lattice modifying element, at least a fluoride of the formula M.sub.II F.sub.2, M.sub.II being a metal of large ionic radius, greater than 1 .ANG., such as those mentioned above. These glasses generally contain up to 45% by moles of fluoride M.sub.II F.sub.2.

Of the glasses of this category there will be cited more particularly those that are free of MF.sub.4 or which do not contain more of it than 5% by moles.

Of the fluoroglasses of this family there will be cited those that contain from 5 to 55% fluoride MF.sub.3, 25 to 65% fluoride MtF.sub.2 and 15 to 45% fluoride M.sub.II F.sub.2.

3. those that contain up to 70% by moles of at least a fluoride MF.sub.4 and up to 60% by moles of at least a fluoride M.sub.1 F.sub.3, M.sub.1 being a metal selected from yttrium, erbium, thulium, ytterbium and lutetium.

These fluoroglasses can further contain as a lattice modifying element in a proportion that can amount to 0 to 30% by moles, at least a fluoride of formula M.sub.II F.sub.2, and/or MtF.sub.2, M.sub.II and Mt being defined as above.

Of the glasses of this family, there will be cited particularly those that contain 25 to 70% fluoride MF.sub.4, 25 to 60% fluoride M.sub.1 F.sub.3, 0 to 30% fluoride M.sub.II F.sub.2 and 0 to 30% MtF.sub.2.

Of the glasses of this category, there will be cited particularly:

those that are free of fluorides MtF.sub.2 or which do not contain more of it than 5% by moles. those that are free of fluorides M.sub.II F.sub.2 or which do not contain more of it than 5% by moles.

The fluoroglasses of the invention and in particular those of the three families that have just been described, can further contain, as adjuvant, in a proportion not exceeding in all 10% by moles, at least, a metal fluoride of the formula M'.sub.II F.sub.2, M.sub.III F.sub.3 or M'F.sub.4, M.sub.III being selected from aluminum, chromium and iron III, M'.sub.II being a bivalent metal different from M.sub.II such as a 3d transition metal (for example, iron, cobalt, nickel) and M' being selected from titanium, hafnium and zirconium.

The invention also has as its object glasses resulting from the mixture of at least two glasses as defined above.

These glasses of the invention can easily be cut and generally resist ambient moisture well. They can be heated, without damage, in the air or under a hydrofluoric acid atmosphere up to temperatures of 250.degree.-350.degree. C. depending on the glass transition temperatures. They can generally be used in installations that can come in contact with products such as fluorine or hydrofluoric acid.

The new glasses of the invention, particularly those with a thorium or yttrium base, exhibit the property, in comparison with fluorozirconate glasses, of having an extremely wide optical window, the widest known for glasses, going 0.25 micron in the ultraviolet to 10 microns in the infrared. Examination of the spectra shows that transparency begins to decrease toward 10 microns to reach still about 65% toward 12 microns.

Moreover, these glasses are very easy to synthesize in large quantity and at very low cost.

The optical properties of the glasses of the invention make it possible to use them especially in optical apparatus, in particular in the infrared region, and also in making optical fibers.

Further, these glasses have good properties of adherence to metals.

The invention also has as its object the process of preparing the glasses defined above. This process is characterized by the fact that the constituent fluorides or corresponding oxides are mixed, in this latter case, with the necessary amount of a fluorinating agent making it possible to transform said oxides into fluorides, by the fact that the mixture of fluorides is melted under a dry, neutral atmosphere, then by the fact that the resulting glass is treated, by the usual methods, to give it the desired shape.

According to a particular embodiment, the molten bath is then tempered by pouring on a brass block then by pressing with a brass cover.

The invention also has as its object fluoride mixtures having the compositions indicated above, obtained as intermediate products in the process of preparing the glasses of the invention.

Of the oxides that can be transformed into fluorides with a fluorinating agent there will be cited, for example, ThO.sub.2, Y.sub.2 O.sub.3, Yb.sub.2 O.sub.3, ZnO, etc.

It will be understood from the preceding description that the invention also comprises the use as glass-forming agent, in the preparation of a fluoride glass free from hydrofluoric acid, of at least one metal fluoride MF.sub.n, wherein n is a number equal to 3 or 4, and M is selected from the group consisting of thorium and uranium when n=4 and yttrium when n=3, and especially in the following cases:

when said glass contains as glass-forming agent, from 20 to 50 mole % of MF.sub.4, and more particularly when said glass also contains from 35 to 60 mole % of a fluoride MtF.sub.2, wherein Mt is a metal selected from zinc and manganese; and wherein said glass also contains as a lattice modifier at least a fluoride M.sub.II F.sub.2, wherein M.sub.II is selected from barium, strontium and lead;

when said glass contains as glass-forming agent from 5 to 55 mole % of YF.sub.3, and more particularly when said glass also contains from 25 to 65 mole % of a fluoride MtF.sub.2, wherein Mt is selected from zinc and manganese; and wherein said glass also contains as a lattice modifier at least barium fluoride;

when said glass contains as glass-forming agents from 25 to 70 mole % of MF.sub.4 and from 25 to 60 mole % of M.sub.1 F.sub.3, wherein M.sub.1 is selected from yttrium, erbium, thulium, ytterbium and lutetium; and more particularly when said glass also contains as a lattice modifier at least one fluoride M.sub.11 F.sub.2 and/or MtF.sub.2, wherein M.sub.II is selected from barium, strontium and lead, and Mt is selected from zinc and manganese.

The following examples illustrate the invention without, however, limiting it.

EXAMPLE 1

A glass having the following composition (in moles) is prepared:

ThF.sub.4 : 40% MnF.sub.2 : 50% BaF.sub.2 : 10%

The operation is as follows:

A mixture having the following composition (in moles) is prepared:

ThO.sub.2 : 40% MnF.sub.2 : 50% BaF.sub.2 : 10% and this mixture is treated with NH.sub.4 F, HF used at the fluorinating agent of the thorium oxide, by using twice the theoretical amount of ammonium acid fluoride. In other words, in this case, 320 moles of NH.sub.4 F, HF are used for 100 moles of the above mixture. The mixture is first brought to 350.degree. C. to fluorinate the oxide, then to 800.degree.-1000.degree. C. to fuse the fluorides.

A brownish yellow glass is obtained.

Similarly, the following (colorless) glasses are prepared (Table 1):

TABLE 1______________________________________ Tg Tc TfExample % in moles .degree.C. .degree.C. .degree.C.______________________________________2 ThF.sub.4 :40 ZnF.sub.2 :40 BaF.sub.2 :20 330 370 6903 ThF.sub.4 :30 ZnF.sub.2 :50 BaF.sub.2 :20 321 353 7024 ThF.sub.4 :40 YbF.sub.3 :40 BaF.sub.2 :20 436 482 7825 YF.sub.3 :30 ZnF.sub.2 :40 BaF.sub.2 :30 339 362 6976 YbF.sub.3 :20 ZnF.sub.2 :50 BaF.sub.2 :30 334 355 697______________________________________

Similarly, the following glasses are prepared (TABLE 2):

TABLE 2______________________________________Example % in moles Color______________________________________ 7 LaF.sub.3 :10 ZnF.sub.2 :60 BaF.sub.2 :30 colorless 8 CeF.sub.3 :10 ZnF.sub.2 :60 BaF.sub.2 :30 colorless 9 PrF.sub.3 :15 ZnF.sub.2 :55 BaF.sub.2 :30 light green10 NdF.sub.3 :15 ZnF.sub.2 :55 BaF.sub.2 :30 purplish pink11 SmF.sub.3 :20 ZnF.sub.2 :50 BaF.sub.2 :30 very pale yellow12 EuF.sub.3 :20 ZnF.sub.2 :55 BaF.sub.2 :25 colorless13 GdF.sub.3 :25 ZnF.sub.2 :50 BaF.sub.2 :25 colorless14 TbF.sub.3 :25 ZnF.sub.2 :50 BaF.sub.2 :25 colorless15 DyF.sub.3 :30 ZnF.sub.2 :45 BaF.sub.2 :25 colorless16 HoF.sub.3 :25 ZnF.sub.2 :50 BaF.sub.2 :25 very pale yellow17 ErF.sub.3 :25 ZnF.sub.2 :45 BaF.sub.2 :30 pink18 TmF.sub.3 :25 ZnF.sub.2 :45 BaF.sub.2 :30 colorless19 LuF.sub.3 :25 ZnF.sub.2 :45 BaF.sub.2 :30 colorless20 UF.sub.4 :70 YbF.sub.3 :30 dark green21 UF.sub.4 :40 YbF.sub.3 :60 green22 UF.sub.4 :50 YbF.sub.3 :40 BaF.sub.2 :10 green23 ThF.sub.4 :33 YbF.sub.3 :33 ZnF.sub.2 :34 colorless24 ThF.sub.4 :50 TmF.sub.3 :40 BaF.sub.2 :10 colorless25 ThF.sub.4 :40 LuF.sub.3 :40 BaF.sub.2 :20 colorless26 ThF.sub.4 :45 ErF.sub.3 :45 BaF.sub.2 :10 pink______________________________________

Similarly, the following glasses are prepared (TABLE 3):

TABLE 3______________________________________Ex-am-ple % in moles TgTc Tf______________________________________27 ThF.sub.4 :30 YF.sub.3 :23 ZnF.sub.2 :32 BaF.sub.2 :15 340 430 64528 ThF.sub.4 :35 YbF.sub.3 :23.5 ZnF.sub.2 :24 BaF.sub.2 :17.5 355 435 661______________________________________

Similarly, the following glasses were prepared: (TABLE 4)

TABLE 4__________________________________________________________________________ Tg Tc TfExample % in moles .degree.C.__________________________________________________________________________29 ThF.sub.4 :40 MnF.sub.2 :55 BaF.sub.2 :5 310 363 64030 ThF.sub.4 :40 MnF.sub.2 :50 BaF.sub.2 :10 326 384 66431 ThF.sub.4 :40 MnF.sub.2 :45 BaF.sub.2 :15 327 376 64732 ThF.sub.4 :35 MnF.sub.2 :55 BaF.sub.2 :10 317 370 65033 ThF.sub.4 :30 ZnF.sub.2 :55 BaF.sub.2 :15 312 325 70634 ThF.sub.4 :30 ZnF.sub.2 :50 BaF.sub.2 :20 321 353 70235 ThF.sub.4 :30 ZnF.sub.2 :45 BaF.sub.2 :25 334 362 72036 ThF.sub.4 :40 ZnF.sub.2 :40 BaF.sub.2 :20 330 370 69037 ThF.sub.4 :45 ZnF.sub.2 :35 BaF.sub.2 :20 339 367 70638 YF.sub.3 :40 ZnF.sub.2 :40 BaF.sub.2 :20 345 385 69839 YF.sub.3 :50 ZnF.sub.2 :30 BaF.sub.2 :20 363 394 72640 ThF.sub.4 :30 YF.sub.3 :30 BaF.sub.2 :10 ZnF.sub.2 :30 338 425 68641 ThF.sub.4 :28.3 YF.sub.3 :28.3 BaF.sub.2 :15 ZnF.sub.2 :28.4 345 425 68642 ThF.sub.4 :26.7 YF.sub.3 :26.7 BaF.sub.2 :20 ZnF.sub.2 :26.6 353 427 68543 ThF.sub.4 :25.5 YF.sub.3 :42.5 BaF.sub.2 :15 ZnF.sub.2 :17 369 42644 ThF.sub.4 :25.5 YF.sub.3 :34 BaF.sub.2 :15 ZnF.sub.2 :25.5 355 42745 ThF.sub.4 :34 YF.sub.3 :34 BaF.sub.2 :15 ZnF.sub.2 :17 366 42946 ThF.sub.4 :34 YF.sub.3 :25.5 BaF.sub.2 :15 ZnF.sub.2 :25.5 337 42947 ThF.sub.4 :32 YF.sub.3 :25 BaF.sub.2 :13 ZnF.sub.2 :30 346 439 68048 ThF.sub.4 :30 YbF.sub.3 :30 BaF.sub.2 :10 ZnF.sub.2 :30 336 423 66349 ThF.sub.4 :29.2 YbF.sub.3 :29.2 BaF.sub.2 :12.5 ZnF.sub.2 :29.1 339 424 66550 ThF.sub.4 :28.3 YbF.sub.3 :28.3 BaF.sub.2 :15 ZnF.sub.2 :28.4 344 426 66551 ThF.sub.4 :27.5 YbF.sub.3 :27.5 BaF.sub.2 :17.5 ZnF.sub.2 :27.5 347 427 66552 ThF.sub.4 :26.7 YbF.sub.3 :26.7 BaF.sub.2 :20 ZnF.sub.2 :26.6 350 422 66153 ThF.sub.4 :40 YbF.sub.3 :30 BaF.sub.2 :0 MnF.sub.2 :30 346 396 67054 ThF.sub.4 :36 YbF.sub.3 :27 BaF.sub.2 :10 MnF.sub.2 :27 356 436 63055 ThF.sub.4 :34 YbF.sub.3 :25.5 BaF.sub.2 :15 MnF.sub.2 :25.5 358 433 63056 UF.sub.4 :50 YbF.sub.3 :40 BaF.sub.2 :10 385 42757 UF.sub.4 :60 YbF.sub.3 :35 BaF.sub.2 :5 379 41258 UF.sub.4 :50 Y F.sub.3 :30 BaF.sub.2 :20 386 43259 UF.sub.4 :40 Y F.sub.3 :35 BaF.sub.2 :25 397 43260 ThF.sub.4 :35 ErF.sub.3 :26.25 BaF.sub.2 :12.5 MnF.sub.2 :26.25 359 422 64461 ThF.sub.4 :35 TmF.sub.3 :26.25 BaF.sub.2 :12.5 MnF.sub.2 :26.25 357 430 63862 ThF.sub.4 :35 YbF.sub.3 :26.25 BaF.sub.2 :12.5 MnF.sub.2 :26.25 358 441 63763 ThF.sub.4 :35 Y F.sub.3 :26.25 BaF.sub.2 :12.5 MnF.sub.2 :26.25 357 423 64064 ThF.sub.4 :40 YbF.sub.3 :30 MnF.sub.2 :30 346 39665 ThF.sub.4 :40 Y F.sub.3 :30 ZnF.sub.2 :30 336 374 750__________________________________________________________________________

The following compositions gave glasses, as shown by X-ray diffraction (TABLE 5):

TABLE 5______________________________________Example % in moles______________________________________66 ThF.sub.4 :47 MnF.sub.2 :43 BaF.sub.2 :1067 ThF.sub.4 :32 MnF.sub.2 :58 BaF.sub.2 :1068 ThF.sub.4 :40 MnF.sub.2 :50 SrF.sub.2 :1069 ThF.sub.4 :40 MnF.sub.2 :50 PbF.sub.2 :1070 ThF.sub.4 :22 ZnF.sub.2 :54 BaF.sub.2 :2471 ThF.sub.4 :42 ZnF.sub.2 :38 BaF.sub.2 :2072 ThF.sub.4 :32 ZnF.sub.2 :43 BaF.sub.2 :2573 ThF.sub.4 :40 ZnF.sub.2 :50 SrF.sub.2 :1074 ThF.sub.4 :40 ZnF.sub.2 :40 PbF.sub.2 :2075 ThF.sub.4 :35 ZnF.sub.2 :45 PbF.sub.2 :2076 UF.sub.4 :40 MnF.sub.2 :50 SrF.sub.2 :1077 UF.sub.4 :40 MnF.sub.2 :50 BaF.sub.2 :1078 UF.sub.4 :40 ZnF.sub.2 :40 PbF.sub.2 :2079 UF.sub.4 :40 ZnF.sub.2 :40 BaF.sub.2 :2080 YF.sub.3 :30 MnF.sub.2 :25 BaF.sub.2 :4581 YF.sub.3 :30 ZnF.sub.2 :30 BaF.sub.2 :4082 YF.sub.3 :40 ZnF.sub.2 :30 BaF.sub.2 :3083 YF.sub.3 :30 ZnF.sub.2 :50 BaF.sub.2 :2084 YF.sub.3 :20 ZnF.sub.2 :40 BaF.sub.2 :4085 YF.sub.3 :10 ZnF.sub.2 :50 BaF.sub.2 :4086 YF.sub.3 : 5 ZnF.sub.2 :60 BaF.sub.2 :3587 YF.sub.3 :15 ZnF.sub.2 :63 BaF.sub.2 :2288 YF.sub.3 :25 ZnF.sub.2 :60 BaF.sub.2 :1589 ThF.sub.4 :28 YbF.sub.3 :28 SrF.sub.2 :16 ZnF.sub.2 :2890 ThF.sub.4 :25 YbF.sub.3 :35 SrF.sub.2 :10 ZnF.sub.2 :3091 ThF.sub.4 :28 YbF.sub.3 :28 PbF.sub.2 :16 ZnF.sub.2 :2892 ThF.sub.4 :25 YbF.sub.3 :35 PbF.sub.2 :10 ZnF.sub.2 :3093 UF.sub.4 :25 YbF.sub.3 :35 SrF.sub.2 :10 ZnF.sub.2 :3094 UF.sub.4 :28 YbF.sub.3 :28 SrF.sub.2 :16 ZnF.sub.2 :2895 UF.sub.4 :28 YbF.sub.3 :28 PbF.sub.2 :16 ZnF.sub.2 :2896 UF.sub.4 :35 YF.sub.3 :35 ZnF.sub.2 :3097 ThF.sub.4 :50 YbF.sub.3 :35 SrF.sub.2 :1598 UF.sub.4 :50 YbF.sub.3 :35 SrF.sub.2 :15______________________________________

Claims

1. A fluoride glass having transparency up to 12 microns consisting essentially of

(1) 5 to 55 mole percent of a fluoride M.sub.1 F.sub.3 as a forming element wherein M.sub.1 is yttrium,

(2) 25 to 65 mole percent of a fluoride MtF.sub.2 wherein Mt is zinc or manganese,

(3) 15 to 45 mole percent of a fluoride M.sub.II F.sub.2 wherein M.sub.II is barium, strontium or lead, and

(4) 0-10 mole percent of an adjuvant consisting of at least one metal fluoride selected from the group consisting of M'.sub.II F.sub.2, M.sub.III F.sub.3 and M'F.sub.4 wherein

M'.sub.II is a bivalent metal different from M.sub.II and Mt,

M.sub.III is selected from the group consisting of aluminum, chromium and iron III and

M' is selected from the group consisting of titanium, hafnium and zirconium,

said fluoride glass being free of hydrofluoric acid as a forming element.

2. The fluoride glass of claim 1 wherein M.sub.II is barium.

3. A fluoride glass having transparency up to 12 microns consisting essentially of

(1) 5 to 55 mole percent of a fluoride M.sub.1 F.sub.3 as a forming element wherein M.sub.1 is yttrium,

(2) 25 to 65 mole percent of a fluoride MtF.sub.2 wherein Mt is zinc,

(3) 15 to 45 mole percent of a fluoride M.sub.II F.sub.2 wherein M.sub.II is barium, and

(4) 0 to 10 mole percent of an adjuvant consisting of at least one metal fluoride selected from the group consisting of M'.sub.II F.sub.2, M.sub.III F.sub.3 and M'F.sub.4 wherein

M'.sub.II is a bivalent metal different from M.sub.II and Mt,

M.sub.III is selected from the group consisting of aluminum, chromium and iron III and

M' is selected from the group consisting of titanium, hafnium and zirconium,

said fluoride glass being free of hydrofluoric acid as a forming element.

4. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 33 mole percent ThF.sub.4, 33 mole percent YbF.sub.3 and 34 mole percent ZnF.sub.2.

5. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 30 mole percent ThF.sub.4, 23 mole percent YF.sub.3, 32 mole percent ZnF.sub.2 and 15 mole percent BaF.sub.2.

6. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 35 mole percent ThF.sub.4, 23.5 mole percent YbF.sub.3, 24 mole percent ZnF.sub.2 and 17.5 mole percent BaF.sub.2.

7. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 70 mole percent UF.sub.4 and 30 mole percent YbF.sub.3.

8. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 40 mole percent UF.sub.4 and 60 mole percent YbF.sub.3.

9. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 40 mole percent ThF.sub.4, 50 mole percent MnF.sub.2 and 10 mole percent BaF.sub.2.

10. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 40 mole percent ThF.sub.4, 40 mole percent ZnF.sub.2 and 20 mole percent BaF.sub.2.

11. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 30 mole percent ThF.sub.4, 50 mole percent ZnF.sub.2 and 20 mole percent BaF.sub.2.

12. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 40 mole percent ThF.sub.4, 40 mole percent YbF.sub.3 and 20 mole percent BaF.sub.2.

13. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 30 mole percent YF.sub.3, 40 mole percent ZnF.sub.2 and 30 mole percent BaF.sub.2.

14. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 50 mole percent UF.sub.4, 40 mole percent YbF.sub.3 and 10 mole percent BaF.sub.2.

15. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 50 mole percent ThF.sub.4, 40 mole percent TmF.sub.3 and 10 mole percent BaF.sub.2.

16. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 40 mole percent ThF.sub.4, 40 mole percent LuF.sub.3 and 20 mole percent BaF.sub.2.

17. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 45 mole percent ThF.sub.4, 45 mole percent ErF.sub.3 and 10 mole percent BaF.sub.2.

18. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 20 mole percent YbF.sub.3, 50 mole percent ZnF.sub.2 and 30 mole percent BaF.sub.2.

19. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 10 mole percent LaF.sub.3, 60 mole percent ZnF.sub.2 and 30 mole percent BaF.sub.2.

20. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 10 mole percent CeF.sub.3, 60 mole percent ZnF.sub.2 and 30 mole percent BaF.sub.2.

21. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 15 mole percent PrF.sub.3, 55 mole percent ZnF.sub.2 and 30 mole percent BaF.sub.2.

22. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 15 mole percent NdF.sub.3, 55 mole percent ZnF.sub.2 and 30 mole percent BaF.sub.2.

23. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 20 mole percent SmF.sub.3, 50 mole percent ZnF.sub.2 and 30 mole percent BaF.sub.2.

24. A hydrofluoric acid free fluoroglass having a transparency up to 12 microns consisting of 20 mole percent EuF.sub.3, 55 mole percent ZnF.sub.2 and 25 mole percent BaF.sub.2.

25. A fluoride glass consisting essentially of

(1) a glass-forming agent consisting of a fluoride MF.sub.4 present in an amount of 20-50 mole percent thereof wherein M is thorium or uranium;

(2) a further glass-forming agent consisting of a fluoride M.sub.1 F.sub.3 present in an amount up to 60 mole percent thereof wherein M.sub.1 is selected from the group consisting of yttrium, erbium, thulium, ytterbium and lutetium;

(3) a lattice modifier consisting of at least a fluoride MtF.sub.2 present in an amount up to 60 mole percent thereof wherein Mt is zinc or manganese;

(4) a further lattice modifier consisting of at least a fluoride M.sub.II F.sub.2 present in an amount up to 30 mole percent thereof wherein M.sub.II is barium, strontium or lead; and

(5) 0-10 mole percent of an adjuvant consisting of at least one metal fluoride M.sub.II 'F.sub.2, M.sub.III F.sub.3 or M'F.sub.4, wherein M.sub.II ' is a bivalent metal different from M.sub.II and Mt, M.sub.III is selected from the group consisting of aluminum, chromium and iron III, and M' is selected from the group consisting of titanium, hafnium and zirconium, said glass being free of hydrofluoric acid.

26. The fluoride glass of claim 25 wherein M is thorium.

27. The fluoride glass of claim 26 wherein M.sub.II is barium.

28. A fluoride glass consisting essentially of

(1) 25-70 mole percent of a fluoride MF.sub.4 glass-forming agent wherein M is thorium or uranium,

(2) 25-60 mole percent of a fluoride M.sub.1 F.sub.3 wherein M.sub.1 is yttrium, erbium, thulium, ytterbium or lutetium,

(3) a fluoride M.sub.II F.sub.2 present in an amount up to 30 mole percent thereof wherein M.sub.II is barium, strontium or lead,

(4) a fluoride MtF.sub.2 present in an amount up to 30 mole percent thereof wherein Mt is zinc or manganese, and

(5) 0-10 mole percent of an adjuvant consisting of at least one metal fluoride M.sub.II 'F.sub.2, M.sub.III F.sub.3 or M'F.sub.4, wherein M.sub.II ' is a bivalent metal different from M.sub.II and Mt, M.sub.III is selected from the group consisting of aluminum, chromium and iron III, and M' is selected from the group consisting of titanium, hafnium and zirconium, said glass being free of hydrofluoric acid.

29. The fluoride glass of claim 28 wherein M is thorium.

30. The fluoride glass of claim 29 wherein M.sub.II is barium.

31. A fluoride glass consisting essentially of

(1) a glass-forming agent consisting of a fluoride MF.sub.4 present in an amount of 20-50 mole percent thereof wherein M is thorium or uranium;

(2) a further glass-forming agent consisting of a fluoride M.sub.1 F.sub.3 present in an amount up to 60 mole percent thereof wherein M.sub.1 is selected from the group consisting of yttrium, erbium, thulium, ytterbium and lutetium;

(3) a lattice modifier consisting of a fluoride M.sub.II F.sub.2 present in an amount up to 30 mole percent thereof wherein M.sub.II is barium, strontium or lead; and

(4) 0-10 mole percent of an adjuvant consisting of at least one metal fluoride M.sub.II 'F.sub.2, M.sub.III F.sub.3 or M'F.sub.4 wherein M.sub.II ' is a bivalent metal different from M.sub.II, M.sub.III is selected from the group consisting of aluminum, chromium and iron III, and M' is selected from the group consisting of titanium, hafnium and zirconium, said fluoride glass being free of hydrofluoric acid.