138La, along with the even rarer 180mTa, is produced in the ν-process, where neutrinos interact with stable nuclei. All other lanthanum isotopes are synthetic: with the exception of 137La with a half-life of about 60,000 years, all of them have half-lives less than a day, and most have half-lives less than a minute. The isotopes 139La and 140La occur as fission products of uranium. Compounds
Lanthanum oxide is a white solid that can be prepared by direct reaction of its constituent elements. Due to the large size of the La3+ ion, La2O3 adopts a hexagonal 7-coordinate structure that changes to the 6-coordinate structure of scandium oxide (Sc2O3) and yttrium oxide (Y2O3) at high temperature. When it reacts with water, lanthanum hydroxide is formed: a lot of heat is evolved in the reaction and a hissing sound is heard. Lanthanum hydroxide will react with atmospheric carbon dioxide to form the basic carbonate.Lanthanum fluoride is insoluble in water and can be used as a qualitative test for the presence of La3+. The heavier halides are all very soluble deliquescent compounds. The anhydrous halides are produced by direct reaction of their elements, as heating the hydrates causes hydrolysis: for example, heating hydrated LaCl3 produces LaOCl.Lanthanum reacts exothermically with hydrogen to produce the dihydride LaH2, a black, pyrophoric, brittle, conducting compound with the calcium fluoride structure. This is a non-stoichiometric compound, and further absorption of hydrogen is possible, with a concomitant loss of electrical conductivity, until the more salt-like LaH3 is reached.
Ichthyosis acquisita is a disorder clinically and histologically similar to ichthyosis vulgaris. : 565

Presentation
Associated conditions
The development of ichthyosis in adulthood can be a manifestation of systemic disease, and it has been described in association with malignancies, drugs, endocrine and metabolic disease, HIV, infection, and autoimmune conditions. : 494 It usually is associated with people who have Hodgkins disease but it is also occurs in people with mycosis fungoides, other malignant sarcomas, Kaposis sarcoma and visceral carcinomas. It can occur in people with leprosy, AIDS, tuberculosis, and typhoid fever. See also
Ichthyosis
Confluent and reticulated papillomatosis of Gougerot and Carteaud
List of cutaneous conditions

References


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