Low-Temperature Heating Systems Control in Low-Energy Buildings

The paper deals with the control of low-temperature heating systems and their responses to changes in indoor environment with the main focus on indoor environmental quality and real energy savings reflecting low-energy buildings energy needs.In relation to energy savings, utilization of low-temperature heating systems is increasing today, in connection with low-temperature heat sources, such as heat pumps. Lower temperature difference between the heating unit and the environment, along with the heat capacity, however, requires better control to be able to make effective response to potential changes in the indoor environment

Recovery of Cerium Dioxide from Spent Glass-Polishing Slurry and Its Utilization as a Reactive Sorbent for Fast Degradation of Toxic Organophosphates

The recovery of cerium (and possibly other rare earth elements) from the spent glass-polishing slurries is rather difficult because of a high resistance of polishing-grade cerium oxide toward common digestion agents. It was shown that cerium may be extracted from the spent polishing slurries by leaching with strong mineral acids in the presence of reducing agents; the solution may be used directly for the preparation of a ceria-based reactive sorbent. A mixture of concentrated nitric acid and hydrogen peroxide was effective in the digestion of partially dewatered glass-polishing slurry. After the removal of undissolved particles, cerous carbonate was precipitated by gaseous NH3 and CO2. Cerium oxide was prepared by a thermal decomposition of the carbonate precursor in an open crucible and tested as reactive sorbent for the degradation of highly toxic organophosphate compounds. The samples annealed at the optimal temperature of approximately 400°C exhibited a good degradation efficiency toward the organophosphate pesticide fenchlorphos and the nerve agents soman and VX. The extraction/precipitation procedure recovers approximately 70% of cerium oxide from the spent polishing slurry. The presence of minor amounts of lanthanum does not disturb the degradation efficiency

Zbržděné lomy v martensitu u ocelí o vysoké pevnosti

samostatný svazek příloh zpracován pod signaturou 33100/1152PrezenčníNeuvedenoNeuveden

Influence of thermal and mechanical treatment on the structure and substructure of TiNi shape memory alloys

V předložené práci byly analyzovány strukturní a substrukturní charakteristiky tří slitin TiNi ( A-Ti-49,5 at.% Ni; B-Ti-50,4 at.% Ni; C-Ti-50,8 at.% Ni) vykazujících tvarově paměťové vlastnosti, které jsou deformačně zpevněny a následně žíhány v teplotním intervalu 300 až 900 °C/1 h/voda. Pro různé stavy matrice byly stanoveny transformační teploty za použití rezistometrické techniky. Po deformaci za studena se mění substruktura martezitu B19' z dvojčatové na dislokační. U slitin B a C byl ve struktuře detekován výskyt R-fáze. Dále byly u slitin C definovány podmínky precipitace Ti11Ni14 a její vliv na modifikaci transformčních teplot. V deformačně zpevněné matrici je omezena mobilita fázového rozhraní B2/B19'. V práci jsou předloženy obecné principy řízeného ovládání teplot fázových přeměn pro různé stavy matric.The contribution is devoted to the analysis of three TiNi-type shape memory alloys containing 49.5 at.% Ni(A), 50.4 at.% Ni(B) and 50.8 at.% Ni(C), respectively. The alloys were work hardened and subsequently annealed at 300 to 900-degrees-C/1 h/water. The transformation temperatures of different materials were evaluated by using of temperature vs. resistance dependences. The martensite B19' changes its morphology after work hardening, the occurrence of R-phase was detected in B and C alloys. Annealing of C alloys led to the precipitation of Ti11Ni14 particles and to the modification of transformation temperatures. The mobility of B2/B19' interface is limited in the case of work hardened alloys. The fundamental principles of the transformation temperatures control are determined

Methods of evaluating local critical states for the initiation of fracture in engineering materials

V práci jsou prezentovány metody hodnocení vzniku lokalizovaných mezních stavů iniciace štěpného a tvárného porušení konstrukčních materiálů se sferoidizovanou strukturou. Základ těchto metod spočívá ve statistické analýze mikrostruktury, ze které jsou následně odvozeny užitím metody nejslabšího článku pravděpodobnosti vzniku lokalizovaného mezního stavu jako funkce vzdálenosti od čela magistrální trhliny a teploty. Metody hodnocení vzniku lokalizovaných mezních stavů byly aplikovány na komerčně vyrobené nízkouhlíkové mikrolegované oceli po kalení a sferoidizačním žíhání. Kvantifikovaný průběh pravděpodobnosti vzniku lokalizovaného mezního stavu iniciace mikrotrhliny odpovídá existenci dvou konkurenčních vlivů, zvětšování homogenně zatíženého elementu objemu a poklesu lokálního napětí s rostoucí vzdáleností od čela magistrální trhliny, a vykazuje proto v závislosti na vzdálenosti od čela magistrální trhliny extrém. Pravděpodobnost vzniku lokalizovaného mezního stavu koalescence dutin s rostoucí vzdáleností od čela magistrální trhliny monotónně klesá.The paper presents methods for assessing the onset of local critical states for the initiation of cleavage and ductile fracture in engineering materials with spheroidized structures. These methods are based on statistical analyses of the microstructure using the "weakest link" approach. This yields the probability of formation of local critical state as a function of the distance from the tip of the main crack and of the temperature. These evaluation methods have been applied to a commercial grade of low-carbon microalloyed steel after its quenching and a spheroidizing annealing. A diagram of the quantified probability, that a local critical state for microcrack formation arises, was found to be affected by two competing influences: the growth of homogeneously stressed elements of volume and the decline of local stresses with increasing distance from the main crack tip. Consequently, this diagram displays a peak at a certain distance from the tip of the main crack. The probability that a local critical state results from the coalescence of voids was found to diminish uniformly with increasing distance from the main crack tip