Annihilation PDF Free Download

J. Weitkamp, H.G.Krvge, H. Pfeifer and W. Hdlderich (Eds.) Zeolites und Relured Microporous Mureriuls: Sure of the Art 1994 Studies in Surface Scicncc and Catalysis, Vol. 83 0 1994 Elsevier Scicncc B.V. All rights reserved.
Poeitron annihilation in Cd+* ion-exchanged and CdS loaded zeolite Y Yuan-Jin He, Yong Hu Department of Physics; Tsinghua University,Beijing 1OOO84, China The lifetime of positron annihilation in Nay, Na(Cd+a)Y, Na(CdS)Y can be decomposed to four components, the third component (2-4ns) ia contributed by Ps trapped in B-cages, while the fourth component (the longest one ) ia an average lifetime of Ps in supercages and more open spaces between zeolite grain particles. By magnetic and 0, quenching one can obtain the Ps lifetime values for B-cage and supercage in NaY zeolite structures, namely 2.71~and 18ns respectively, which are reasonably close to what expected by 'free volume model'.
1.INTRODUCTION Increasing activities have been aimed at the development of intrazeolite semiconductor quantum dots materials [I1. In developing a reproducible way to load semiconductor dots into the accessible void spaces of zeolite host lattices, the direct information of the occupancy of different cages in a zeolite is important. As one of sensitive microprobe of voids on nanometer scale, positron annihilation has been used to characterize zeolite-based materialsC2-e1. In zeolite materials positrons can be slowed down internally and form para-or otho-positronium (p-Ps,o-Ps). The lifetime of self-annihilated o-Ps is very long in vacuum (*134ns), but in zeolite cages, it will be shortened by pick-off annihilation which ia an annihilation process of the the positron in o-Ps with a surrounding electron. In principle, free volume of each kind of cages could be well correlated to Ps lifetime and the changes of intensities of corresponding lifetime
components could give the information about the extent of semiconductor dots loading. In previous works two longest lifetime components ( T T *) have been observed in zeolite Y, but it is still arguable whether T a or T is responsible to Ps annihilation i n 0 cage or supercage. In this paper we report on the results of positron annihilation in ion-exchanged zeolite Y and CdS loaded zeolite Y. We found that T a is responsible to Ps annililation in 0-cage and positron annihilation may be a very interesting technique to characterize intrazeolite materiala. 2. EXPERIMENTAL
Zeolite NaY powder was employed as the starting material for preparing Na(Cd+2)Y and Na(CdS)Y. Cd+2 impregnating was carried out in Cd(N08), solutions. The NaY powders were soaked i n Cd(N08), solution of different concentrations. The pH values of the solutions were adjusted to 6. The concentrations were selected i n that way so that the ratio of the total amounts of Cd(N08), in the solutions over the weights of NaY zeolite powders are 0.07, 0.21, and 0.48 mol/Kg respectively. After being pre-heated, the powders were sintered at 4OOC in O1 for 12 hours. In order to load CdS molecules into the zeolite cages, gaseous H2S was used. The extent of CdS loading can be controlled by the pressure and flow rate of HIS gas. In this work HIS gas was obtained by reaction of FeS with dilute HC1 solution. The loading process lasted about 2 hours, the colours of the zeolites changed from white at the begining to yellow progressively. Positron lifetimes were measured in a fast timing system with a time resolution of -3OOps. In order to determine the lifetime values with a reasonable accuracy, two time windows were chosen: 0.4nslchannel for T *, the longest lifetime, and O.lns/channel for T T and T a. The longest lifetime was obtained by 3-component free fitting of the lifetime spectra taken with O.4ns/channel time window and then was inputed as the fixed T~ component in 4-component fitting of the spectra taken with O.lns/channel time window.
In general, 4 components could be resolved from the lifetime spectra of positron annihilation in intrazeolite materials used in this study. Typically T is about 0.2118, which is mainly due to p-Ps annihilation, T is about 0.66-0.76ns, which is due to the annihilation of positrons bounded to the zeolite grain surface, T a (3-4118) and T (16-70ns) are both due to o-Ps pick-off annihilation, this is convinced by magnetic quenching and oxygen quenching experiments of this study. 3.1 Magnetic quenching In order to confirm the nature of the long lifetimes, positron annihilation lifetime was measured on Nay, Na(Cd+)Y, and Na(CdS)Y samples under different intensity of magnetic field. The p-Ps state is a singlet state I O,O> with m=O, where m is the magnetic quantum number, while o-Ps state has three components I l,l>,I 1,0>, and 11, -1> (m=1, 0,-1) respectively. Under finite magnetic field I O,O> and 11, O> are mixed and the lifetime of I1,0> o-Ps state is decreased to 1 X ’ *lo+x2 X p 4 where X o( X ), is the o-Ps (p-Ps)annihilation rate at zero-field, and x is the magnetic field intensity devided by the internal magnetic field of Ps. In zeolites, the o-Ps lifetime will be decreased further via pick-off annihilation even at zero-field. In fact there was no significant magnetic effect on 1 a, since 1 8 is dominated by a relatively high pick-off annihilation rate and the lifetime decreasing hy magnetic quenching was not pronounced. But for T the magnetic quenching effect is very clear (see Fig.1). Among the three components of o-Ps, only 11, O> state will be quenched by magnetic field, while positrons annihilated from other two thirds will not affected by magnetic field at all. Therefore in analysing data we took T and 214/3 of the longest lifetime of the zero-field spectrum as the fixed parameters, and looked the variation of the so obtained second longest lifetime T 4’ with magenetic fields. When pick-off rate is small, T 4’ can be roughly viewed as I 1, O> o-Pe lifetime .
60 n
Fig.1 The lifetime T 4' (see text) ae a function of magnetic field for Nay( 0 ),Na(Cd+2)Y (0.2lmol/Kg) ( 0 ), and Na(CdS)Y (O.almol/kg)(A).
In Fig. 1 one can see that the lifetime of I1,0> state of o-Pa can be magnetically quenched. The different 1 4' values at zero-field for Nay, Na(Cd+)Y, and Na(CdS)Y samples indicate that positronium pick-off annihilation rate is different in different samples. These data may relate to the size of free volume in the sample and also to the local chemical environment where Ps annihilated. The T ~ ' lifetime decreased very rapidly at low field, and saturated at about 1OkG. The ultimate lifetime at strong magnetic quenching seems around 6ns. This may explain why magnetic quenching on 1 8 (3-4ne) was not observable.
3.2 Oxygen quenching Fig.2 and Fig.3 show the Os quenching effect observed in this work. Both 1 a and 1 have undergone big changes upon introducing oxygen since oxygen has unpaired electron which leads the positron in o-Ps annihilate with the electron of opposite spin
v H m
0 1
0 2
0 3
0 6
Fig. 2 Variation of lifetime and intensity of 3rd component vs. concentration of ion-exchanged (a) and of CdS loaded (b) Zeolite Y: (.)lifetime in 0,; (U)lifetime in vacuum; (A)intensity in vacuum; (A)intensity in 0,.
0 O
0 1
I 0 2
I 0 3
0 4
0 6
0 1
0 2
0 s
Fig. 3 Variation of lifetime and intensity of 4th component VB.concentration of ion-exchanged (a) and of CdS loaded (b) Zeolite Y: (0)lifetime in vacuum; (.)lifetime in 0%; (A)intemity in vacuum; (A)intensity in O1.
According to free volume model'c71, the Pa lifetime has a linear relation to the cavity volume as : s -7.80V +1.29 (ns) (1) where V is the free volume in unit of . For NaY zeolite the volume of 8-cage is 0.16(nm)s, then the lifetime of Pa located in B -cage should be 2.611s according to equation (l), this value is very close to the T a value observed in Nay, 2.7ns. Therefore it is reasonable to contribute T a to positronium annihilation in B -cage. From Fig.2 one can see that 1 a increases with the concentrations of Cd+2 ions. This effect could simply explained by the increasing of the volume of B-cage when the two Na' ions were replaced by one Cd+2 ion. A rough estimation of the volume of B-cage of ion -exchanged Y zeolite could be made according to equation (1) and But this point needs to be our data, the 'value is 0.31 clarified by more examination since other possibilities, for instance, the uncertainty of data manipulation, may also have to be put into account. The lifetime of Pa in supercages is expected to be 14ns according to free volume model (eq.(l)), but what we observed in NaY i n is an average value of the vaccum is -70ns, implies that T lifetime of Ps in supercages, and Ps in some more open space, e.g., the free volume between small zeolite grain particlea. Interesting fact is that,the Pa lifetime when quenched with O2 becomes -18ns for NaY zeolite and Na(Cd+2)Y samples. From this fact one would suggest that O2 quenching is very effective to Pa located in open space between zeolite particles and is not effective to Ps trapped in supercages, and that the lifetime of Ps trapped i n supercage is about 18ns, which is reasonably close to the prediction of free volume model'. The big difference between the results for Na(Cd+=)Y and for and L for Na(CdS) Y samples is the additional decreasing of T latter case with CdS concentration increasing (see Fig.3). This can easily be explained by suggesting that CdS molecules are more effective than Cd+z in bloking the free volume in supercages and the open space between particles so as to reducing positronium
formation. In conclusion, all these results indicate that positron annihilation will be a very promising microprobe to characterize intrazeolite materials.
REFERENCES [l] G.A.Ozin, Adv. Matter. 4 (1992) 612. [2] K. Venkateswaran, K. L. Cheng and Y. C. Jean, in Positron Annihilation (World scientific Publ.Co., Singapore) (1986), P.199. [3] M. Debowska, J. Ch. Abbe and G. Duplatre, Phys. Stat. Sol.(b) 146 (1988) 91. [4] Y. Ito, T. Takano and M. Hasegawa,Appl. Phys.,A46 (1988) 193. [6] Y. Ito, M. Hirose and Y. Tabata, Appl. Phys., As0 (1990) 39. [6] 2. Gao, X. Yang, J. Cui, Y. Wang, Zeolites, 11 (1991) 607. [7] Y. C. Jean, T. C. Sandreczki and D. P. Ames, J. Polym. Sci B, (1986) 1247.

Tomb of Annihilation PDF is part of the Ultimate Pack, a bundle of classic D&D products that have stood the test of time. When you buy this package, you get the Lord of the Rings Starter Set, the Mystical Illumination Sourcebook, the Unbound Landscape Sourcebook, and the Unfulfilled Rage Card Sets. All of these are important parts of any serious D&D campaign. With a little work, you can increase your party size and have more fun playing D&D. This article will give you a quick overview of how to use each of these products to expand your playtime and make the game more interesting.

Annihilation: A Novel - Ebook written by Jeff VanderMeer. Read this book using Google Play Books app on your PC, android, iOS devices. Download for offline reading, highlight, bookmark or take notes while you read Annihilation: A Novel. Books for downloads Mass Effect: Annihilation 588 English version by Catherynne M. Valente Overview Mass Effect: Annihilation by Catherynne M. Valente An official tie-in to the hit video game Mass Effect: Andromeda, written by award-winning and New York Times bestselling author Catherynne M. Valente An official tie-in to the hit video.

Annihilation PDF Free Download

Tomb of Annihilation PDF The Lord of the Rings Starter Set has everything you need to create your own kingdom in Tomb of annihilation. You start with a humble village that lives in the shadows of Mount Doom. When you reach level one, you gain possession of the Wooden Horse, a unique mule. Your only means of travel is through the mystical tunnels, guarded by the creatures of Gorgoroth. The fate of your village rests on your ability to keep Gorgoroth at bay and kill all of its spawn.

Tomb of Annihilation PDF Free Download

Pdf free

Total Annihilation Download Free

At character generation time, choose your race and select an evil character as your villain, if you choose one at character generation. You’ll immediately be presented with several possible races, each one with a few different options. You’ll also be presented with two different paths for your villain’s quest, both straight and secret. The secret path takes you through the ruin of Mt. Doom, but you’ll also find yourself encountering other players and enemies along the way.

After choosing your race and starting your journey through tomb of annihilation, you enter the Lengthening Rift. Inside are many hazards, including the ever present lava lamps, that must be avoided. When you’re at a safe spot, a magical orb will activate, inflicting damage on characters and creatures and casting a death curse on the player. Fortunately, it’s possible to break the curse with the help of another player, or with help from the other adventurers in your party. This is how you advance through the campaign storyline.

Tomb of Annihilation PDF Free Download

Once you kill all the lava lizards, you can proceed to the next part of the tomb of annihilation adventure, the Shattering the Skystone. This is a very difficult mission, where you and your three other characters must defeat a dragon, a massive boss. Upon defeating the dragon, you’ll be teleported back to the surface, where you’re ready to continue on with the rest of your group. The Shattering the Skystone is another part of the tomb of annihilation game and introduces players to a new group of characters who must work together to defeat a final boss.

Tomb of annihilation pdf free download

The best bit of adventure in the tomb of annihilation is its overall graphics and music. The game’s visuals are pretty much like what you would expect from a turn-based dungeon crawler, with excellent cel-shading and lots of bright, vibrant colors. The music is just as impressive, with scores that range from being mildly annoying to genuinely exciting.

Annihilation Jeff Vandermeer Pdf Free Download

tomb of annihilation offers up plenty of, too. If you played the original (and really, who does? ), you’ll find that each level and each mission offer multiple paths through the mission, which means that you can repeat some scenes to gain experience or pick up on a new strategy for tackling the challenge on a fresh day. Best of all, however, is the way that the storyline threads are intertwined and built upon with a steady flow of new characters and scenarios throughout the course of your adventure.

If you enjoyed the original Tomb of Obliteration as much as I did when I played it for Halloween several years ago, you’re in luck. The fifth edition is currently out, and it’s bringing the best parts of the game’s original release and adding a few fresh surprises. All in all, it’s a great action-adventure game that scratches the itch for a good dungeon-crawler. Charming graphics, excellent voice acting, excellent writing–it’s no surprise this series is still one of my favorites.


Tomb of Annihilation PDF Free Download

Annihilation PDF Free Download