In particular, this is due to the possibility of conducting experiments in space. A large number of studies on convection in the melt during the growth of single crystals were done by various methods. Hydrodynamic phenomena are typical of the floating zone method [ 13 - 15 ]. It should be noted that phenomena of convection are studied by two ways: convective phenomena experimentally investigated by physical modeling of the crystal growth in transparent liquids and by constructing mathematical and computer models.
Mathematical models tend to represent a complex system of differential equations. Main assumptions in constructing models are stationary, two-dimensional and axisymmetric of the hydrodynamic problem [ 13 ]. Characteristic of models is the extensive use of dimensionless criteria of similarity theory. Particular attention is paid to thermocapillary convection Marangoni convection [ 15 ].
Results of model experiments and calculations are used to explain some properties of single crystals of molybdenum, so that study is considered in more detail. Convective flows in the melt can have a significant impact on the structure and properties of the growing single crystal. Important parameters such as impurities and the concentration and temperature gradients in the melt are dependent on nature of flows.
The shape of the crystal-melt interface appears to depend not only on heat transfer processes, but also on conditions of the melt flows. Consider the most important similarity criteria which give a relation between the convective and diffusive heat and mass transfer. Therefore, it can be expected that microsegregation in the crystal melt is associated with hydrodynamics of the melt.
X-ray topograms and autoradiograms of longitudinal cross-sections of samples showed characteristic bands enriched with impurities. If we assume that the melt is the incompressible fluid, the density of which depends on the temperature and impurity content, the forces, that give rise to convective flows in the melt, are the following: gravitational forces cause natural convection , capillary forces cause Marangoni convection and inertial forces occur when the crystal is rotated.
In general, flow patterns in the molten zone are the result of the joint effect of these forces. Before discussing the problem of convection we should consider features of the temperature distribution in the molten zone. The interfacial crystal-melt surface at the crystallization front has a temperature T 0. Furthermore, there is the negative radial gradient directed from the periphery toward the center of the zone.
As for radial temperature gradients, they correspond to Rayleigh numbers, almost equal to zero. If on the free melt surface the temperature gradient exists, resulting in changes in surface energy, then capillary Marangoni forces begin to act. These forces give rise to characteristic convection in the melt.
With increasing the distance from the surface the rate decreases and then changes its sign. In the case of the zone melting Marangoni forces act on the periphery of the zone from its middle to interphase boundaries. In the absence of rotation, Marangoni flow in the melt is toroidal axially symmetric. With increasing Bo outer vortices increasingly dominate over the lower ones. This leads to the non-uniform transfer of impurities in the melt and eventually to the radial non-uniformity of impurities.
Increase in the dislocation density in the crystal can be explained by the interfacial surface curvature produced by convection. This leads to such defects in the crystal as impurity bands which is found at the respective longitudinal sections of the X-ray topographs [ 15 ]. Temperature fluctuations lead to reduction of K eff and further to macrosegregation. The banded heterogeneity may disappear at growth rates below a certain critical value due to fairly good diffusion in the solid phase.
We must also mention the detected submicroporosity in molybdenum single crystals grown by EBFZM after the first and second zone runs. These submicropores of diameter 0. For the first time in , Dash [ 16 ] has grown dislocation-free silicon single crystals from the melt using the method of a narrow waist or a neck.
He believed that dislocations appeared from the seed in the waist region, come to the surface, and stresses, occurring during further growth, cannot generate dislocations, if initially they did not exist in the crystal. Since dislocation defects are non-equilibrium, they may only be a consequence of non-equilibrium growth conditions. According to [ 1 , 2 , 15 ], for the formation of dislocations are responsible: external stresses of mechanical origin; thermal stresses; local stresses due to concentration gradients; condensation of vacancies; local stresses due to inclusions; errors during growth.
Thermal stresses, occurring during the growth of single crystals from the melt, lead to significant increase in the dislocation density. Application of dislocation theory and theory of internal stresses to the problem of the crystal growth has led to significant achievements. It is shown that the main source of stresses causing deformation and dislocation multiplication in the growing crystal is the inhomogeneous temperature field.
From this it follows that the crystal growth is necessary to strive to ensure that the temperature field in the growing crystal should be as close as possible to the linear one, so T z ' ' would be minimal. Due to this, the dislocation density has been reduced by almost two orders of magnitude. Note that growing single crystals of metals with the low dislocation density is significantly harder than single crystals of semiconductors or dielectrics.
This is due to the fact that elastic constants of metals go to zero much faster as the temperature approaches the melting point [ 9 , 10 ]. The structural perfection of single crystals grown from the melt is influenced not only by the temperature gradients themselves, but the important factor in this respect is the cooling rate which is implemented at the stage of the crystal growth itself, and then under cooling to room temperature [ 17 ]. An influence of growth conditions on the dislocation substructure of copper single crystals is investigated in [ 18 ].
At a regular control of the dislocation structure, the Cu single crystals are grown from the melt at the rate of 0. With an increase in the growth rate an average size of subgrains is significantly reduced from 5x10 -2 cm to 0. On the basis of these experiments, the conclusion is made that the model of the sub-boundaries formation is valid, and impurities do not play any significant role in the formation of the substructure in copper single crystals of purity less than History of the development of EBFZM method to produce refractory metals in the single-crystal form has more than seventy years [ 19 , 20 ].
Over the past thirty years there was a significant progress both in improving experimental techniques used for growing single crystals of refractory metals, and the study of their structure and properties. Then, the most advanced electron-beam guns are presented in [ 21 - 24 ]. There have been developed and tested the original EBFZM set-ups for growing single crystals of refractory metals.
In the design of these set-ups have been successfully resolved the main problems concerning the mechanisms of the movement of the cathode assembly, the electron gun, the power supply and others Figure 1. Single crystals, bicrystals and tubular crystal of many transition and refractory metals were grown using the electron guns with the protected annular filament-cathode in EBFZM set-ups.
A principle of operation of EBFZM set-ups with annular electron guns, in a certain extent, is similar to a function of the vacuum triode: the tungsten filament cathode , the feed sample anode , focusing electrodes control grid , the melting chamber housing. The voltage, current and power, which are consumed for melting the feed, refining the liquid metal and growing the single crystal, are determined not only by both the anode voltage and the current of the cathode filament, but also by the residual gas pressure in the cathode-anode gap.
In EBFZM set-ups for operation of the electron gun is very important the gas release from the feed during melting. Any sudden rise in pressure due to the gas release, metal evaporation or local vacuum decay even to 10 -1 Pa in the electron gun lead to avalanche of a low resistance of the anode-cathode system and even to complete destabilization of the electron gun.
From the above there are basic requirements to EBFZM set-ups providing conditions for the stable zone melting: stability of the electron gun; stability of the power supply; perfection of moveable nodes; an impurity homogeneity of the feed, otherwise it can cause unpredictable sharp increase in pressure in the melting chamber. It should be noted that the most sensitive element of EBFZM set-ups is the electron gun, so the focus of this section will be paid to the designs of electron guns, which should create the optimal and stable over time temperature field.
Electron guns in many EBFZM set-ups have some disadvantages that prevented widespread of the method and demanded a lot of efforts to correct them. Typically, the designs of all known guns are such that spatters and vapors of metal get to the cathode filament, thereby destabilizing functions of the gun, changing its power due to local decrease in emissivity of the cathode filament.
This often leads to burnout of the cathode and to finish the growing process. Another disadvantage of existing electron guns is contamination of the feed and crystal by metal vapors from which the cathode is made usually tungsten , and the electron gun itself. Such contamination is most likely when the cathode is located in "line of sight" visibility of the feed, which is typical for almost all designs of electron guns. At K the rate of evaporation of tungsten is less than 2x10 g s -1 cm -2 and thermionic tungsten cathodes are sufficient to melt all metals.
Three-electrode electron guns with a single accelerating electrode allow to stabilize power supplied to the zone and to eliminate variations of the temperature during the growing process. It was also assumed that accelerating electrodes could act as modulators of the anode current, which would maintain without inertia the given heat regime and have significant advantages compared with known control systems.
Naturally, electron guns, in which the upper and lower borders of focusing are realized by mechanical devices, do not meet these requirements. Benefits of both EBFZM set-ups and electron guns [ 20 ] compared to previous ones consisted in the fact that metal vapors and spatters cannot reach the cathode and the liquid zone because the cathode filament is outside of a "line of sight". Main criteria for using new guns in EBFZM set-ups are: simplicity of the design, as well as reliability of operation at high temperatures and intensive sputtering.
The density of the electron flux from the filament with the current leads nearby is for times higher as compared with the opposite side of the same filament without the current leads nearby. Such asymmetry of electron fluxes is observed in all guns in which the ring filament is made of two semi-rings. The asymmetric distribution of the electron density causes an asymmetry of the temperature field in the liquid zone and, as a result, the asymmetry of heating of the growing crystal.
By the way, this may be one of reasons for the "snap" growth of single crystals. Apparently, the heterogeneous structure, which is characterized by a layered distribution of both impurities and defects, is a consequence of a mismatch of the thermal axis and the axis of the growing crystal. One of the main practical conclusions is that, despite an apparent lack of difference between one- and two-element cathodes, only a singleton cathode in the form of the loop provides satisfactory symmetry of the electron flux and temperature field.
It contributes to the problem of obtaining homogeneous single crystals with the reproducible structure and crystallographic characteristics along the entire length. The basic requirements that determine conditions for the stable operation of the electronic guns and, especially, EBFZM set-ups can be formulated as follows: an absence of sputter on the filament, i.
The liquid zone 10 on the single-crystalline rod 4 is produced by the electron beam 9 emitted from the tungsten filament cathode 1. Focusing is carried out by the electron gun 2. The power supply provides the accelerating voltage of 25 kV and the anode current up to 1 A. A lack of positive feedbacks between the cathode and the anode in the electron gun allows maintaining the average power of the electron beam, which is almost constant throughout the growing single crystals or bicrystals. Random power fluctuations with a frequency of several hertz do not exceed 0.
Metallographic examinations of the crystal structure at the macro and micro levels provide extensive qualitative and quantitative information about the structure [ 22 - 24 ]. A possibility exists to measure of various structural elements up to 1 micron. The dislocation density in the crystal can be evaluated according to the number of etch pits per unit area in the event that it does not exceed 10 8 cm An interference attachment to a metallographic microscope gives a possibility to evaluate the surface roughness of cross-sections.
The polarization console allows detecting inclusions of the second phase in a sample, if the latter is present in significant amounts. To carry out metallographic studies the sample must first be cut off from the corresponding bulk single crystal and then prepared by grinding. Cutting samples of molybdenum and tungsten single crystals of necessary geometry and crystallographic orientations can be produced by the electroerosion device.
It is well known that this technique can produce a significant damage of the sample surface - to a depth of about microns. When this happens, the surface contamination and defects lead to increase of dislocations in the surface layer, but also there appear a typical network of cracks extending to a considerable depth. After cutting, all the above defects must be removed by both the mechanical grinding and polishing. Then, the cold-worked layer should be removed by chemical etching and electropolishing at the optimal conditions. However, it is necessary to keep in mind two things.
First, all etchants are divided into two large groups. The first group has a pronounced orientation effect, i. In general, the etching figures revealed by these etchants have nothing with the outgrowth of dislocations. The second group represent etchants to produce etch pits, revealing the outgrowing low-angle boundaries and individual dislocations.
But even in this case to speak about one correspondence of etch pits and dislocation is not correct, it requires evidences in each case. With regard to detection of the microstructure of tungsten and molybdenum crystals is, for example, a commonly known Murakami etchant 10 g NaOH, 30 g of K 3 Fe CN 6 , g of H 2 O which has a strong orientation effect, although it is also identifies some low-angle boundaries. It turns out that the etchant "works" not only to identify dislocations, but also to reveal dislocations introduced into the crystal as a result of plastic deformation at the surface with a prick of the diamond indenter.
Furthermore, this etchant identifies sub-boundaries with small misorientation angles and thus it has been widely used to detect the substructure of molybdenum and tungsten single crystals, grown from the melt by EBFZM. For metallographic studies the optical microscopes and automatic analyzer are used. The latter is widely used for the quantitative metallographic analysis of the linear substructure: the subgrain size distribution along and across the crystal, the dislocation density inside the subgrains averaged at least for 20 fields of view, and by the stereometric metallographic analysis as well.
It is known that in many cases some low-angle boundaries can be qualitatively compared by misorientation angles. In other words, it is a qualitative determination, where misorientation angles of neighboring subgrains are more and where — less, because aA quantitative determination of misorientation angles by metallographic methods is impossible.
To obtain such information on the real structure of the crystal it is necessary to use methods of X-ray diffraction microscopy. Here, to obtain the quantitative information about misorientation angles of the substructure elements of molybdenum and tungsten single crystals we used both the X-ray topograms of angular scanning and X-ray recording by the wide divergent beam. Especially clear for determining misorientation angles is the method of the X-ray wide divergent beam [ 25 ]. On the X-ray record of the perfect crystal, free of low-angle boundaries, Kossel lines are solid curves of the second order.
In the block crystal, recording through the low-angle boundary between adjacent subgrains, the orientation changes abruptly and Kossel lines contain gaps. Of serious interest is the question about what kind of dislocations occurs during growth from the melt? It rises from the standpoint of a study of physical aspects of the crystallization process.
Most of disclocations are assembled into grids and walls as a result of poligonization processes and form the characteristic substructure. Such dislocation ensembles consisting of growth dislocations are also of interest. To undertake such a research on the real crystal structure the most suitable method is transmission electron microscopy, which allows determining the type of dislocations, their Burgers vectors and crystallography of low-angle boundaries. It means that the volume, occupied by actual low-angle boundaries, is negligible.
Observation of low-angle boundaries of such samples would require at least 10 times more samples taking into account that a really observable surface of a sample has an area of about 5 micron 2. Naturally, to prepare samples having such little hope of success is a real Sisyphean task. Therefore, a method of preparation of foils is used, which provides a hole in a specified area in vicinity of low-angle boundaries. An essence of the method is as follows. On one side of the original sample in a form of the washer of diameter 3 mm and thickness of 0.
Then, on this side of the sample a protective film of a clearcoat in the simplest case — a collodion is applied to the surface and thoroughly dried. Next by the microhardness recorder PMT-3 using a diamond indenter the protective layer is violated in the right place or a series of injections or scratches and by electropolishing a recess of a required depth is received. Optionally, this set of operations might be repeated. It should only be kept in mind that in the process of the electropolishing all of dislocations should be removed from the surface layer of the sample, introduced there by the action of the indenter.
Thereafter, the varnish is removed from the sample surface by using an organic solvent acetone, ether and the electropolishing is performed from the reverse side of the sample before the formation of holes. As mentioned before, the presence of significant amounts of impurities has a significant impact on the structure and properties of the crystals, and for molybdenum and tungsten the greatest impact on the properties is made by interstitial impurities, primarily carbon, which is characterized by very low solubility limits in the solid state at room temperature [ 26 ].
Therefore, the analysis of the chemical composition and purity control of single crystals is an important part of the characterization of a material. The content of impurities is shown in Table 1. The purity of metals is also checked by a residual resistivity at liquid-helium temperatures, since at low temperatures the main mechanism of the carriers scattering in metals is scattering on impurities [ 29 ]. Here, the ratio of resistivities at room and liquid-helium temperatures is defined by the non-contact and four-contact methods.
Metals and their alloys in the polycrystalline state represent a set of randomly oriented crystallites, or grains, which separated by high-angle boundaries. Properties of polycrystalline materials that are widely used conventionally in materials science and technology largely depend on the size and crystallographic orientation of the constituent grains and, consequently, on the properties of boundaries between the grains.
In recent years a number of theoretical and experimental studies of the interface boundary structure, the energetic and regularities of the grain boundary diffusion and high-temperature creep, the segregation of impurities and structural defects at the interface, as well as processes of heterogeneous nucleation at the interface during phase transitions, is significantly increased [ 29 ].
For an experimental investigation of the above phenomena, it is desirable to have samples with well known or readily determinable geometrical relationships between crystallites. From this point of view, of course, the interfaces in bicrystals with known crystallographic parameters are the most convenient and preferable objects.
Growing methods of metal bicrystals can be divided into two main groups. The first one includes methods in which oriented bicrystals can be grown from two oriented seeds using standard methods of Chalmers, Czochralski, Bridgman or zone recrystallization. The second group includes methods in which the interphase boundary is obtained by sintering together two plates of oriented single crystals. It should be noted that both groups of methods allow receiving both twist and tilt boundaries, as well as mixed ones.
Consider the specific advantages and disadvantages of both groups. There is a lot of information on getting oriented bicrystals of various metals and alloys by sintering or diffusion welding [ 30 - 48 ]. Using this method to obtain bicrystals usually leads to the fact that boundaries contain a substantial amount of pores and oxide inclusions. Upgraded versions of the method are used to produce bicrystals of copper, silver, nickel, copper-indium and copper-arsenic alloys. In this case, the boundary turns out fairly flat, and does not contain inclusions of the second phase; although sometimes on the boundary an emergence of a small stray of grains of arbitrary crystallographic orientations have been found.
Furthermore, disks prepared for sintering should be flat and have a surface roughness of not more than 0. It is clear that before sintering the electropolished deformed surface layer should be removed, otherwise recrystallization becomes inevitable and qualitative boundaries cannot be obtained.
Bicrystals of low-melting-points metals can be grown using the method from other group. The essence is that bicrystals can be grown from the melt with the help of two correctly oriented seeds causes no problems at all. Somewhat more complicated is the situation in this way to grow bicrystals of refractory metals such as molybdenum, tungsten, niobium, tantalum, vanadium, etc. There is information on growing niobium bicrystals by arc zone melting method [ 40 ].
However, this technique does not permit to obtain the required stability of the molten zone and the symmetry of the temperature gradients in the melt and in the solid phase.
The Formation of Snow Crystals | American Scientist
This leads both to an increased density of dislocations and low quality of the grown bicrystals. The original method of growing bicrystals of niobium by electron-beam zone melting is described in [ 38 ]. The essence of this method consists in the following. The single crystalline seed of a cylindrical shape partially cut along a plane of symmetry parallel to the growth axis .
Next by moving apart the halves of the original single-crystal seed typed at the desired misorientation angle of the boundary of the bicrystal to grow. Then the bicrystal can be grown simultaneously from both halves of the seed. Thus, the niobium bicrystals of diameter of 6. In our opinion, this technique of growing bicrystals, though captivating by its simplicity, but it is too "capricious", on which, however, suggest the authors themselves. They managed to get good bicrystals in only one case out of four.
In our view, the failure of the following causes: a poor quality of the electron gun in heating and a complexity of the adjustment of the Y-shaped seed in the thermal zone. Another method of producing bicrystals of refractory metals is described in [ 30 ]. The essence of this simple method is as follows: on single-crystal rods the molten zone is created.
Then after rotation of the base bar to the desired angle the zone is "frozen". For all its simplicity and attractiveness of this technique it is also not free from shortcomings. First, a small size of a boundary: no more than a diameter of the rod; secondly, the boundary is wavy, as it turns out not as a result of the joint growth of two neighboring grains, but as a result of the "collapse" of moving towards each other two crystallization fronts whose profile in the process of EBFZM is substantially non-planar.
In our opinion, the most suitable melting technique for obtaining bicrystals of refractory metals with bcc lattice, which do not undergo phase transitions in the solid state, is only EBFZM. This technique allows obtaining a necessary stability of the molten zone and the axial temperature gradient, as well as the required symmetry of the radial temperature gradients. The latter condition is largely ensures a stability of the growth process of bicrystalline boundaries when growing simultaneously from two seeds oriented in a predetermined manner [ 36 , 39 ].
Stability of the growth of the grain boundary in bicrystals simultaneously from two seed crystals oriented in the predetermined manner, largely due to the symmetry and uniformity of the temperature field. Based on structural features of EBFZM set-up, we would like to note some highlights that should be considered when growing bicrystals of pure refractory metals: 1 the stability and radial uniformity of the power supplied by the electron gun; 2 the co-axiality of the growing bicrystal and electron gun coincidence of thermal and geometric axes or centers in the liquid zone ; 3 the uniformity of the heat removal from the growing bicrystal through the elements of the seed and bicrystal.
Experiments are carried out on growing bicrystals without rotation, but it turned out that this may affect even minor violations of the local temperature profile in the liquid zone, resulting in one of the growing crystals in the bicrystal can die out.
Growth of organic crystals via attachment and transformation of nanoscopic precursors
At first, to prepare the parts for the seeds the initial single crystal should be cut by the electroerosion into cylinders of 20 mm long Figure 2. The cylinders are cut by the diametrical plane to segments for the purpose of obtaining the desired misorientation angle. The segments of the bicrystalline seed are chemically etched in a mixture of hydrofluoric and nitric acids. Bicrystalline seeds are produced by combining the single-crystalline segments e.
Another method of preparing the seeds is that one of the segments further cut at an angle equal to the misorientation angle of the bicrystal to grow. This method proved to be a little bit easier, because it does not require additional operations of the orientation of single crystals. In cases where, besides the misorientation angle, the defined crystallographic parameters should also have the bedding plane of the grain boundary, the plane is defined with respect to which the boundary should be symmetrical.
Then a cut is made along a plane that is separated from it by an angle equal to half of the misorientation angle of the bicrystal to grow. Later the plane of the contact between two segments of the bicrystalline seed should be the grain boundary of the growing bicrystal. In the process of the zone growing the grain boundary remains strictly specified and parallel to the axis of the bicrystal and to the axes of both single-crystalline halves of the seed.
Our experience has shown that these procedures of preparing bicrystalline seeds are the most important and sufficient for the reproducible growth of bicrystals with any misorientation angle. Bicrystals are of 30 mm in diameter and of mm long Figure 3.
A correct preparation of bicrystalline seeds and a compliance of the optimal temperature distribution allow avoiding pinching one grain by another. The visual and metallographic examinations of bicrystalline samples show that the grain boundaries are macroscopically flat over large areas and do not contain "parasitic" grains or the second phase inclusions.
Tendency of undoped refractory metals of Group 6 molybdenum, tungsten to intergranular embrittleness do not only create difficulties in processing, but also significantly reduce the scope of their practical use [ 32 ]. Because of complexity of grain boundaries in polycrystalline samples, containing a large and, to some extent, uncontrollable set of grains, studies are carried out on specially prepared bicrystals with well-known crystallographic parameters, because they are the most convenient model objects for the grain boundaries studies.
In [ 30 , 32 , 36 , 49 ], the dependence of the strength of grain boundaries in molybdenum bicrystals is revealed on the type of boundaries and the misorientation angle between the grains. It is proved that the twist boundaries in the molybdenum bicrystals are more brittle compared to the tilt ones [ 41 , 42 ]. True, in both types of boundaries twist and tilt the possible influence of the bedding plane of the grain boundaries is not taken into account.
It should be noted that in the polycrystalline ingots of molybdenum are usually found all types of boundaries and the misorientation angles in different sections of the ingots vary widely. The main reason for the different behavior of the high- and low-angle grain boundaries is the nature of the interaction of these boundaries with impurity atoms.
Apparently, impurity atoms by a reaction with the low-angle boundaries are located on their constituent dislocations, whereby the low-angle boundaries occur at areas with a reduced content of impurities. At the high-angle boundaries the impurities segregate more evenly along the boundary, strongly weakening a grip of grains.
Therefore, there is an increased susceptibility to intergranular embrittlement. The embrittlement of cast or recrystallized molybdenum largely depends on the interstitial impurities carbon, oxygen, nitrogen , which, due to the low solubility in the crystal lattice, are allocated along the grain boundaries [ 41 - 46 ]. However, it remains unclear why there is the "critical" content, the more that the solubility of carbon and oxygen in molybdenum is by several orders of magnitude lower. Also unclear is the question, what is the relationship between the total content of interstitial impurities in molybdenum and the content of second phase carbides, oxides at the grain boundaries.
Using the molybdenum bicrystals in studies of grain boundaries usually encounter with serious difficulties in getting bicrystals of given crystallographic parameters, as well in preparing a sufficiently large number of reproducible bicrystalline samples from the same bicrystal. Apparently, one of the essential crystallographic parameters of the samples is the bedding plane of the grain boundaries, which are still obtained by chance, since the known methods do not allow to grow the molybdenum bicrystals with any desired plane boundary.
In the bicrystalline twist boundaries the axis of twist uniquely determines the plane of the grain boundary. The widest range of the bedding planes of the grain boundaries can be obtained at bicrystals with the tilt boundaries when at one axis in the case of the symmetrical boundaries can exist two bedding planes and in the case of asymmetric boundaries - of any number. In [ 36 , 46 ], the strength of the bicrystalline twist and tilt boundaries in molybdenum bicrystals is studied depending on the misorientation angle between two grains and on the bedding plane of the grain boundary i.
In [ 46 ], the molybdenum bicrystals are grown by the method, the main feature of which is the existence of the optimal temperature distribution in the liquid zone. The samples with twist boundaries are prepared as described in [ 47 , 48 ], but for the growth the better electron gun is used, which allows to create the very narrow liquid zone on the sample and, consequently, more even grain boundaries.
In the grown bicrystals the symmetric tilt boundary  lies along the plane , and the twist boundary - along Also, the bicrystals with the tilt boundaries  are grown, which are intended for similar studies. The initial single-crystalline rods, from which the bicrystals are then grown, are prepared in two ways. First, the molybdenum bicrystals Mo-1 are of a standard purity see Table 2. Secondly, for comparison, the molybdenum bicrystals Mo-II of highly-pure molybdenum are grown. Bicrystalline samples are tested for strength by the three-point bend device the rate of deformation 0.
The distance between supports is 9 mm, the radius of supports and the knife - 1 mm. Besides, there may be some parameters and attributes that we still do not understand to be important or parameters too difficult to measure. There may even be parameters as yet undiscovered. Although the examples discussed in this paper may represent some of the extreme cases and perhaps rare occurrences, it is not difficult to envision that any IgG clone can show a modest level of undesirable attributes that can easily be overlooked unless they are disastrous.
Therefore, it will continue to be a challenge for us to determine—of all physicochemical diversities possible—the range of attributes that are favorable, acceptable, and unacceptable as antibody therapeutics. With new alternative Ig-like protein modalities on the horizon, the technologies of recombinant Ig expression will continue to feed opportunities for cell biologists to investigate biological processes of secretory protein biosynthesis and secretory pathway trafficking as well as the protein recycling events in the endocytic pathway.
Hasegawa thank Drs.
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National Center for Biotechnology Information , U. Int J Cell Biol. Published online Mar 5. Author information Article notes Copyright and License information Disclaimer. Department of Therapeutic Discovery, Amgen Inc. Received Dec 12; Accepted Jan This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article has been cited by other articles in PMC. Abstract Recombinant immunoglobulins comprise an important class of human therapeutics. Introduction Immunoglobulins Igs are the important mediators of humoral immunity. Historical Perspectives on Russell Body Phenotype: Mott Cells, Morular Cells, and Grape Cells Aberrant intracellular globules in lymphocytes and plasma cells have captivated cell biologists for more than a century.
Hybridoma Cell Lines as a Model System to Study RB Biogenesis The establishment of hybridoma cell lines that spontaneously develop RBs enabled a detailed cellular characterization and biochemical analysis on their compositions in vitro. Roles of the Variable Domain Sequences in Russell Body Formation The potential importance of variable domain sequences in determining the RB propensity was first discussed in by two groups [ 56 , 67 ].
Open in a separate window. Figure 1. Figure 2. Dissecting the Roles of HC and LC in RB Formation In homologous experimental systems, a sustained expression of full-length HCs in the absence of LC synthesis turns out to be difficult because of the proteotoxicity that eradicates such cell population, combined with the cellular mechanisms that delete CH1 domain to circumvent the toxicity [ 49 ]. Implications of Differential RB-Inducing Propensities for Therapeutic Antibody Discovery Research The differential RB-inducing properties among different Ig clones are likely to be governed by the intrinsic physicochemical properties embedded in the VH and VL domain sequences, although in some studies the HC isotypes also influenced the threshold.
ER Storage: Crystallization at the Site of Immunoglobulin Synthesis Since the first report on crystalline bodies CBs in by Glaus [ 79 ], intracellular crystals associated with plasma cells and lymphocytes have been documented from a variety of human pathological sources such as plasmacytoma, myeloma, and chronic lymphocytic leukemia as well as non-Hodgkin's lymphoma [ 80 ]. Figure 3. Implications of the Crystalline Body Formation for the Therapeutic IgG Screening and Expression Strategy Unlike the numerous examples of unfolded protein accumulation in the ER that triggers severe ER stress responses [ , ], accumulation of correctly folded proteins in the ER has not been well studied in animal cells.
Crystal-Storing Histiocytosis Crystal-storing histiocytosis CSH is another example where Igs crystallize in the lysosomes of histiocytes, or macrophages, in the bone marrow, spleen, liver, lymph nodes, lung, and other organs [ — ]. Roles of Differential Physicochemical Properties in the Extracellular Fate of Immunoglobulins Physicochemical properties of individual Igs will inevitably influence the fate of individual Ig clones differently in the extracellular space upon secretion. Amyloidogenic Immunoglobulins: Light-Chain Amyloidosis and Heavy-Chain Amyloidosis Amyloidosis is a disease of protein misfolding where soluble secreted proteins aggregate into insoluble fibrils which are then deposited to tissues to cause functional and structural organ damage [ , ].
Cryocrystalglobulinaemia and Extracellular Immunoglobulin Crystals In cryocrystalglobulinemia [ ], not only can the culprit monoclonal Igs crystallize in the cytoplasm of plasma cells that express them, but the secreted counterpart of the same Ig clone also deposits as extracellular crystals, thereby believed to cause microvasculature lesions and to impair renal functions [ , ]. Synthesis of Engineered IgGs and Antibody Fragments Applications of histidine-based pH-sensitive target binding functions in therapeutic antibodies have gained popularity in recent years [ , ].
Conclusion and Prospective Nearly every aspect of Ig structure and function can be engineered to improve selected properties to a desired level, to confer additional effector functions, or even to eliminate undesirable attributes. Acknowledgment H. References 1. Tonegawa S. Somatic generation of antibody diversity.
Berek C, Milstein C. The dynamic nature of the antibody repertoire. Immunological Reviews. Russell W. An address on a characteristic organism of cancer. British Medical Journal. The parasite of cancer. The Lancet. Inclusion bodies in experimental herpetic infection of rabbits. The Journal of Experimental Medicine. Michels NA. The plasma cell.
A critical review of its morphogensis, function and developmental capacity under normal and under abnormal conditions. Archives of Pathology. McConnell G, Lang A. Russell's fuchsin bodies. The Journal of Medical Research. Pearse AG. The nature of Russell bodies and Kurloff bodies; observations on the. Journal of Clinical Pathology. Lisco H. Russell bodies occurring in the lymph follicles of the intestinal tract of pigs. Anatomical Record. Gray A, Doniach I. Ultrastructure of plasma cells containing Russell bodies in human stomach and thyroid. Iwamoto T, Witmer R. Light and electron microscopy on plasma cells and Russell bodies in the iris of a chronic uveitis patient.
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Diagnostic Cytopathology. In vivo crystallization of human IgG in the endoplasmic reticulum of engineered chinese hamster ovary CHO cells. Journal of Biological Chemistry. Sensors and regulators of intracellular pH. Nature Reviews Molecular Cell Biology. The pH of the secretory pathway: measurement, determinants, and regulation.
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Head and Neck Pathology. Growth of Mg2TiO4 single crystals by the floating zone method; I. Crystal Growth: an introduction by editer P. Determination of the phase diagram by the slow cooling float zone method: the system Mg-O-TiO2. Shindo J. Crystal Growth 50 Ref. The technical report for the "Gas Guide". Some technical information can be found here.