摘要:
The invention relates to a process for the preparation of aerogels having hydrophobic surface groups, consisting ofa) taking a silicate-type lyogel,b) optionally subjecting the lyogel taken in Step a) to a solvent exchange with another solvent,c) surface-modifying the gel obtained in Step a) or b) with at least one C.sub.1 -C.sub.6 -alcohol, andd) drying, under subcritical conditions, the surface-modified gel obtained in Step c).
摘要:
The invention concerns a process for preparing organically modified aerogels, in which a) a silicic acid sol with a pH .ltoreq.4.0 is produced from an aqueous potassium silicate solution using at least one organic and/or inorganic acid; b) the resultant silicic acid sol is polycondensed by the addition of a base to form SiO.sub.2 gel; c) the gel produced in step b) is washed with an organic solvent until the water content of the gel is .ltoreq.5 wt %; d) the gel obtained in step c) is surface-modified with at least one C.sub.1-6 alcohol; and e) the surface-modified which are difficult to dissolve in the silicic acid sol. Before step b), the resultant salts, which are difficult to dissolve, are precipitated to the greates possible extent and separated from the silicic acid sol.
摘要:
An inorganic material comprising an aerogel, a process for its preparation, and its use. The invention relates to a composite material comprising from 10 to 95% by volume of aerogel particles whose particle diameter is less than 0.5 mm and a phyllosilicate as inorganic matrix material.
摘要:
The invention relates to a process for producing modified, fiber-reinforced xerogels having porosities greater than 60% and xerogel matrix densities below 0.6 g/cm.sup.3 and to their use as thermal insulating material.
摘要:
The invention relates to a switching device comprising at least one feeding circuit provided for DC power supply to at least one subscriber's terminal unit. The feeding circuit is especially provided for digital subscribers' terminal units. The invention furthermore relates to the feeding circuit used. There is proposed to provide a first and a second limiting circuit. The first limiting circuit comprises a first series combination of a first supply transistor arrangement and a first supply resistor arrangement to limit a supply current flowing through the first series combination. The second limiting circuit comprises a second series combination of a second supply transistor arrangement and a second supply resistor arrangement to limit a supply current (Is) flowing through the second series combination. A potential (V0) present on the control input of the second supply transistor arrangement depends on the voltage (Ur) present on the first series combination.