Patent Publication Number: US-7596305-B2

Title: Method and apparatus for preparing vaporized reactants for chemical vapor deposition

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a division of application Ser. No. 10/376,894 filed Feb. 28, 2003, now U.S. Pat. No. 6,827,974 which claims priority of U.S. provisional Application 60/369,110, filed on Mar. 29, 2002,which is hereby incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to a method and apparatus for preparing vaporized reactants, and more particularly, to a method and apparatus for preparing vaporized reactants for chemical vapor deposition with a magnetically driven, seal-less motor. A gas may act as a barrier to prevent the vaporized reactants from communicating with other components of the vaporization apparatus. 
   BACKGROUND OF THE INVENTION 
   Typically, coated glass articles are produced by continuously coating a glass substrate while it is being manufactured in a process known in the art as the “float glass process.” This process involves casting glass onto a molten tin bath which is suitably enclosed, then transferring the glass, after it has sufficiently cooled, to lift out rolls aligned with the bath, and finally cooling the glass as it is advanced across the rolls initially through a lehr and thereafter while exposed to the ambient atmosphere. A non-oxidizing atmosphere is maintained in the float portion of the process, while the glass is in contact with the molten tin bath, to prevent oxidation. An air atmosphere is maintained in the lehr. The chemical vapor deposition of various coatings may be conveniently performed in the bath or the lehr, or even in the transition zone therebetween. 
   The physical form of the reactants employed in glass coating processes is generally a gas, liquid, solid, vaporized liquid or solid, liquid or solid dispersed in a barrier gas mixture, or vaporized liquid or solid dispersed in a barrier gas mixture. The chemical vapor deposition process generally employs a vaporized liquid or solid, which is typically dispersed in a barrier gas mixture. 
   Chemical vapor deposition processes are well known in the art of coating glass substrates. For example, U.S. Pat. No. 5,090,985 discloses a method of preparing vaporized reactants by injecting a liquid coating precursor into a vaporization chamber and heating the precursor until it turns into a vapor. Simultaneously, a blend gas is admitted into the chamber and thoroughly mixed with the vapor. A set of mixing blades, in direct mechanical engagement with a motor, rotate inside the vaporization chamber and distribute the liquid precursor as a uniform, thin film onto the vaporization chamber walls. The vaporized precursor and blend gas mix and become a stream of vaporized reactants for pyrolytic decomposition at the surface of a hot substrate. 
   Typically, one or more seals are located between the motor and the vaporization chamber to prevent precursor vapor from reaching the motor. For example, at least one seal is typically located around the shaft connecting the mixing blades with the motor. The seals are designed to exude small amounts of oil. The oil, however, may mix with the precursor thereby contaminating the precursor. Also, the seals may fail due to dirt particles becoming located between the seal and the shaft. The particles cause the shaft and the seal to vibrate and the vibrations eventually cause the seal to weaken and fail. If a seal fails, large amounts of oil may leak into the vaporization chamber and/or precursor vapor may leak into the seal oil. 
   Magnetically driven motors are well known in the art for rotating an object without a direct mechanical connection between the motor and the object. Typically, the absence of a direct mechanical connection eliminates the need for drive shafts and seals around those shafts. For example, U.S. Pat. Nos. 4,790,911 and 4,913,777 disclose the use of a magnetically driven motor to rotate a container without a direct mechanical connection between the motor and the container. 
   U.S. Pat. No. 4,913,777 teaches a container having a closure with a driven magnet affixed thereto. A driving magnet is located outside the closure. Upon engagement of the driving magnet with the driven magnet, the closure is rotated thereby distributing solvent about the inside surface of the closure. The walls of the closure are heated resulting in the formation of a vapor of the solvent. 
   The rotation of the closure cannot, however, distribute a uniform, thin layer of precursor material on the entire inside surface of the closure. Additionally, the container of the &#39;777 patent does not allow for the continuous and uniform addition of precursor and other gases into the closure typically required for chemical vapor deposition preparations. 
   It must be noted that the prior art referred to hereinabove has been collected and examined only in light of the present invention as a guide. It is not to be inferred that such diverse art would otherwise be assembled absent the motivation provided by the present invention. 
   Therefore, it would be desirable to have a magnetically driven means for mixing and consistently distributing the precursor material on the inside of the vaporization chamber. It would also be desirable to create a barrier between the corrosive vaporized reactants in the vaporization chamber and other components of the apparatus with a barrier gas. 
   SUMMARY OF THE INVENTION 
   The present invention is directed toward a method and apparatus for preparing vaporized reactants, useful, for example, for chemical vapor deposition onto hot substrates. In accordance with the present invention, it has been discovered that vaporized reactants can be prepared with: 
   1) one or more coating precursors wherein said precursors are metal or silicon compounds at a temperature above their melting points but substantially below their standard vaporization temperatures, thereby causing said coating precursors to be in the form of a liquid; 
   2) a magnetically driven portion having driver and driven magnets and a structure to align said magnets; 
   3) a vaporization chamber having at least one inlet for continually injecting said liquid coating precursors into said chamber to produce a vapor; 
   4) a barrier portion adjacent said magnetically driven portion having a gas located therein; and 
   5) a structure for distributing said liquid precursors in said chamber, said structure in communication with said magnetically driven portion through said barrier portion. 
   In an alternative embodiment, vaporized reactants can also be prepared with: 
   1) one or more coating precursors wherein said precursors are metal or silicon compounds at a temperature above their melting points but substantially below their standard vaporization temperatures, thereby causing the coating precursors to be in the form of a liquid; 
   2) a magnetically driven motor portion having driver and driven magnets and a structure to couple said magnets; 
   3) a vaporization chamber having at least one inlet for continually injecting said liquid coating precursors into said chamber to produce a vapor; 
   4) a structure for distributing said liquid coating precursors in said chamber, said structure in communication with said motor portion. 
   The present invention provides a substantially contaminant-free stream of a coating precursor vapor. Because there are no seals to fail, the likelihood of oil leaking into the vaporization chamber is eliminated as is the possibility of precursor vapors leaking into the seal oil. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
       FIG. 1  is a schematic side view of the present invention, including a vertical cross-sectional view of a vaporization chamber and a magnetically driven portion; 
       FIG. 2  is a schematic side view of an alternative embodiment of the present invention; 
       FIG. 3  is a schematic view of a structure to couple the driver and driven magnets of said magnetically driven portion; 
       FIG. 4  is a schematic side view of a portion of a shaft passing through a chamber; and 
       FIG. 5  is a schematic cross-sectional side view depicting an alternative embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless the claims expressly state otherwise. 
   Referring now to  FIGS. 1 and 2 , an apparatus  10  for carrying out the invention is depicted having at least one preheating vessel  12 , equipment illustrated generally at  14  for the introduction of a gas  16  into the apparatus  10 , equipment illustrated generally at  18  for the introduction of a barrier gas  20  at least into a barrier portion  22 , a seal-less, magnetically driven portion  24 , a vaporization chamber  26 , and a structure  28  for distributing a precursor material  30  uniformly within the vaporization chamber  22 . 
   The vaporization chamber  26  is a vessel enclosed by one or more walls  32  and having a liquid zone  34  and a vapor zone  36 . A horizontal thin film evaporator, such as for example by Artisan Industries, Inc., of Waltham, Mass., having the product designation “One-Half Square Foot Rototherm E,” provides a suitable vaporization chamber  26  for the present invention. The boundary between the zones  34 ,  36  is indicated generally by line  38  in  FIGS. 1 and 2 . The liquid zone  34  is defined as the area within the vaporization chamber  26  in which the wall  32  of the vaporization chamber  26  is coated with a liquid coating precursor  40 , while the vapor zone  36  is defined as the area within the vaporization chamber  26  where the liquid coating precursor  40  has been completely converted to a vapor  42 . The location of the boundary  38  between the liquid zone  34  and the vapor zone  36  will vary depending on the volatility of the particular precursor material  30  being used, the vaporization chamber  26  temperature, mass flow rate of the barrier gas  20 , etc. Thus, when using a precursor material  30  having a relatively high volatility, the vaporization chamber  26  will have a relatively large vapor zone  36 . 
   The precursors materials  30  of the present invention are either liquids, which exert a vapor pressure at room temperature, or solids which, when heated above room temperature but below their standard vaporization temperatures, become liquids which exert a vapor pressure at those elevated temperatures. By “standard vaporization temperature” as used herein it is meant the temperature at which the vapor pressure of the pure liquid component is equal to one atmosphere. In either case, the precursor materials  30  in the present invention are initially heated in the preheating vessel  12  to temperatures above their melting points but substantially below their standard vaporization temperatures. Typically, the precursor materials  30  are preheated to a temperature from about 70° F. to 530° F. At such temperatures the precursor materials  30  become volatile liquids which are well below their decomposition temperatures. By the term “substantially below the standard vaporization temperature” as used herein it is meant a temperature which is from 10° to 90° F. below the standard vaporization temperature of a compound (the coating precursor), such that thermal decomposition of the heat sensitive compounds is greatly reduced. 
   A precursor material  30  may be initially heated by any conventional apparatus known in the art for heating solids or liquids, such as fired or electrical resistance heating or steam jacketing of the preheating vessel  12  containing the precursor material  30 . Although only one heating apparatus is depicted in  FIGS. 1 and 2 , additional heating apparatuses for one or more precursor materials (not shown) may be added without departing from the scope of the invention. The liquid coating precursor  40  is communicated into the liquid zone  34  of the vaporization chamber  26  though at least one inlet  44 . Preferably, the at least one inlet  44  is adjacent a bottom portion  46  of the vaporization chamber  26  and allows the liquid precursor  40  to be continuously and uniformly injected into the chamber  26 , as depicted in  FIGS. 1 and 2 . 
   Suitable precursor materials  30  useful for practicing the present invention include, without limitation to those specifically recited, dimethyltin dichloride, tetraethoxysilane, diethyltin dichloride, dibutyltin diacetate, tetramethyl tin, methyltin trichloride, triethyltin chloride, trimethyltin chloride, tetrabutyl titanate, titanium tetrachloride, titanium tetraisopropoxide, triethylaluminum, diethylaluminum chloride, trimethylaluminum, aluminum acetylacetonate, aluminum ethylate, diethyldichlorosilane, methyltriethoxysilane, zinc acetylacetonate, zinc propionate, or mixtures thereof. These compounds are generally well known in the art of chemical vapor deposition (CVD) technology, as precursors for applying coatings on hot glass. The invention will work equally well for any precursor material  30 , or mixtures thereof, that exert a vapor pressure. A preferred precursor material  30  for depositing tin oxide is dimethyltin dichloride, or a mixture of dimethyltin dichloride and methyltin trichloride, for example 95 weight percent dimethyl tin dichloride and 5 weight percent methyltin trichloride. 
   The vaporization chamber  26  is heated by conventional means such as, for example, fired or electrical resistance heating or steam jacketing  48 . In this way, the temperature of the vaporization chamber  26  is constantly maintained, and the heat necessary for vaporization of the liquid precursor  40  is provided. Typically, the contents of the vaporization chamber  26  are maintained at a temperature from about 95° F. to 550° F. 
   The magnetically driven portion  24  has at least one driver magnet  50  and at least one driven magnet  52 . The driver magnet  50  is connected to a motor shaft  54  which extends from a motor  56 .  FIGS. 1 and 2  only schematically depict that connection. In one preferred embodiment depicted in  FIGS. 1 and 2 , the driven magnet  52 , is located radially inward from the driver magnet  50 . The driven magnet  52  is completely sealed within a chamber  58  from the driver  50  and is connected to the structure  28  for distributing precursor material  30  uniformly within the vaporization chamber  26 . The two magnets  50 ,  52  are coupled through one or more walls  60  of the chamber  58  such that upon rotation of the driver magnet  50 , the driven magnet  52  and the structure  28  are turned without physical contact between the magnets  50 ,  52 . 
   The shape, size and orientation of the driver  50  and driven  52  magnets are only schematically depicted in the Figures. Those skilled in the art understand that magnets of various shapes, sizes and orientations may be utilized without departing from the scope or spirit of the present invention. 
   Typically, the driver magnet  50  has one or more banks of high strength permanent magnets (not shown). The driven magnet  52  may have corresponding banks of similar magnets, which cause it to rotate in synchronization with the driver magnet  50 . Alternatively, the driven magnet  52  may have an arrangement of copper bars, which cause it to follow the driver magnet  50  at a slightly lower speed. 
     FIG. 3  schematically depicts a structure to precisely align the driver  50  and the driven  52  magnets shown in  FIGS. 1 and 2 . The driver  50  magnet has an inside surface  62  which has been machined precisely to the dimensions of the motor shaft  54 . The driver magnet  50  also has an outside surface  64  which has been precisely machined to have a constant radius  66 . Machining the inside  62  and outside  64  surfaces of the driver  50  magnet allows the magnet  50  to rotate at a constant radial distance  66  about the shaft  54 . An outside surface  68  of the driven magnet  52  is also machined to have a constant radius  70 . 
   A collar  72 , having a first  74  and a second  76  machined surface, is also depicted in  FIG. 3 . The collar  72  fits over the driver  50  magnet and the second machined surface  76  is securely attached to an end plane  78  of the motor  56 . The first machined surface  74  of the collar  72  is attached to the chamber  58  housing the driven  52  magnet. The driver  50  magnet rotates at a constant velocity at a constant radius  80  from the driven magnet  52 , thereby allowing the magnets  50 ,  52  to engage through a uniform and constant magnetic field  82 , as depicted in  FIGS. 1 and 2 . The uniform and constant magnetic field  80  between the magnets  50 ,  52  causes the driven magnet  52  to rotate constantly and uniformly. The constant and uniform rotation of the driven magnet  52  rotates the structure  28  for distributing liquid coating precursor  40 , depicted for example in  FIGS. 1 and 2 , in the same manner resulting in a uniform and thin film of liquid coating precursor  40  being located on the walls  32  of the vaporization chamber  26 . 
   As shown in  FIGS. 1 and 2 , the structure  28  for distributing precursor material within the vaporization chamber has a shaft  84  connected to the driven magnet  52 . One or more mechanical wipers or blades  86  are connected to the shaft  84  and extend into the vaporization chamber  26  through the barrier portion  22 . The shaft  84  is supported by at least one friction reducing device, such as a bearing ring  88 . Preferably, the shaft  84  is supported by a first  88  and a second  90  bearing ring, as depicted in  FIGS. 1 and 2 . The bearing rings  88 ,  90  have a plurality of ball bearings  92  located therein and allow the shaft  84  to be rotatably supported within the vaporization chamber  26 . At least the second bearing ring  90  is supported in place by a bearing ring support structure  94  having a plurality of ports  96 . 
   The mixing shaft  84  preferably turns the mechanical wipers or blades  86  to uniformly propel the liquid coating precursor  40  with centrifugal force against an inner wall  98  of the vaporization chamber  26 . The liquid coating precursor  40  forms a uniform layer  100  on the inner wall  98  where it vaporizes and produces a steady stream of concentrated precursor vapor  42 . 
   As depicted in  FIG. 1 , the barrier gas  20  is communicated from the equipment  18  through at least one barrier gas line  102  into the chamber  58  of the driven magnet  52 . The barrier gas  20  flows through the ports  96  within the bearing ring support structure  94 . From the ports  96 , the barrier gas  20  flows into the barrier portion  22 . In the preferred embodiment, the barrier portion  22  includes the driven magnet chamber  58 , at least the second bearing ring  90  and at least a portion of the vaporization chamber  26 . 
   In an alternative embodiment, depicted in  FIG. 2 , the driven magnet chamber  58  has at least one aperture  104  substantially adjacent the shaft  84  which communicates the barrier gas  20  from the chamber  58  into the barrier portion  22 . As depicted in  FIG. 4 , the aperture  104  has a slightly larger diameter  106  than an outside diameter  108  of the shaft  84 . The shaft  84  is located through the aperture  104  thereby leaving a gap  110  around the shaft  84 . The gap  110  allows the barrier gas  20  to flow from the chamber  58  and into the barrier portion  22 . 
   Regardless of the means selected to communicate the barrier gas  20  from the chamber  58  into the barrier portion  22 , both of the above described embodiments allows for the continuous and uniform addition of barrier gas  20  into the vaporization chamber  26 . 
   Preferably, the barrier gas  20  is continuously communicated from the chamber  58  into the barrier portion  22  at a velocity which is greater than the diffusion velocity of the precursor vapor  42 . Typically, the greater velocity of the barrier gas  20  is provided by pressurizing the barrier gas  20 . The communication of a barrier gas  20  into the barrier portion  22  at a velocity greater than the diffusion velocity of the precursor vapor  42  prevents the precursor vapor  42  from communicating from the vaporization chamber  26  into the barrier portion  20 . The greater velocity of the barrier gas  20  also prevents the corrosive precursor vapor  42  from reaching the bearing rings  88 ,  90  or the magnetically driven portion  24 . 
   The barrier gas  20  may be, for example, helium, nitrogen, hydrogen or argon, mixtures thereof, or any other barrier gas  20  which is chemically inert with the precursor vapor  42  at the temperatures involved, as well as mixtures thereof. Preferred blends of gasses are helium and nitrogen, and mixtures thereof. The barrier gas  20  is stored in cylinders  112  and piped through regulators  114 , flow meters  116  and valves  118  into the chamber  58 , as shown in  FIGS. 1 and 2 . 
   The barrier gas  20  is communicated into the barrier portion  22  at a temperature below the ambient vaporization chamber temperature. Means (not shown) to modify the delivery temperature of the barrier gas  20  injected into the barrier portion  22  may be used. The lower temperature of the barrier gas  20  cools the bearing rings  88 ,  90  and prevents, or greatly reduces, the decomposition of the rings  88 ,  90  as a result of heat. 
   If desired, any amount of the gas  16  may be communicated into the liquid zone  34  of the vaporization chamber  26  through at least one inlet  120  in the vaporization chamber  26 . The gas  16  increases the mass transfer of the precursor vapor  42  from the vaporization chamber  26 . This increase in mass transfer of precursor vapor  42  causes accelerated vaporization of the liquid precursor  40 . 
   The gas  16  injected into the liquid zone  34  may be the same as the barrier gas  20  discussed above or it may be helium, nitrogen, hydrogen, argon, mixtures thereof or any other chemically inert gas. The gas  16  to be injected into the liquid zone  34  is stored in cylinders  122  and piped through regulators  124 , flow meters  126  and valves  128 . Means (not shown) to modify the delivery temperature of the gas  16  injected into the vaporization chamber  26  may be used. 
   An alternative embodiment of the present invention is depicted in  FIG. 5 .  FIG. 5  depicts a driven magnet  130  adjacent a driver magnet  132 . The driver magnet  132  is connected by a shaft  134  to a rotating motor  136 . The driven magnet  130  is located within a vaporization chamber  138  that separates the driver magnet  132  from the driven magnet  130  yet allows them to magnetically couple. The chamber  138  prevents precursor vapor  140  from communicating with the motor  136 . Preferably, the driven magnet  130  is selected to withstand the high temperatures associated with the vaporization chamber  138 . For example, a driven magnet  130  having a temperature and chemical resistant resin coating  142 , such as those known to those skilled in the art, may be used. The driver  132  and driven magnets  130  and the vaporization chamber  138  are designed and operate substantially as described above. 
   The driven magnet  130  is formed with one or more wipers or blades  144  as depicted in  FIG. 5 . Upon the coupling of the driver magnet  132  with the driven magnet  130  through one or more walls  146  of the vaporization chamber  138 , rotation of the driver magnet  132  rotates the driven magnet  130 . Rotation of the driven magnet  130  turns the wipers or blades  144  inside the vaporization chamber  138  to uniformly propel liquid precursor  148  with centrifugal force against an inner wall  150  of the vaporization chamber  138 . 
   The blade  144  is rotatably supported by at least two friction reducing devices within the vaporization chamber  138 . Preferably, the friction reducing devices are temperature and chemically resistant bushings, or bearings  152 . The bushings  152  may be constructed out of, for example, carbon or Teflon®, or other materials known to those skilled in the art for their chemical and temperature resistance. 
   If desired, a barrier gas  154  is communicated from cylinders  156 , regulators  158 , flow meters  160  and valves  162 , substantially as described above, into the vaporization chamber  138  to increase the mass transfer of the coating precursor vapors  140  from the vaporization chamber  138 . A precursor material  164  is initially heated, as described above, and communicated as a liquid into the vaporization chamber  138  through at least one inlet  166 . 
   In both of the above described embodiments, the liquid precursor  40 ,  148 , coating precursor vapor  42 ,  140 , and barrier gas  20 ,  154  (if present) are heated inside the vaporization chamber  26 ,  138  to a temperature greater than the temperature of the injected liquid precursor  40 ,  148  but still below the coating precursor standard vaporization temperature. The temperature to which the components are heated will be determined by the thermal decomposition characteristics of the particular coating precursor used and the mass flow rate of the chosen barrier gas  20 ,  154 . The liquid precursor  40 ,  148  and chemical composition of the barrier gas  20 ,  154  as well as their respective rates of introduction into the vaporization chamber  26 ,  124  must be selected together, such that a sufficient amount of barrier gas  20 ,  154  is present to cause an increase in the mass transfer of the vaporized precursor  42 ,  140  thereby accelerating the vaporization of the liquid precursor  40 ,  148 . In this manner, the liquid precursor  40 ,  148  is completely vaporized at a temperature below its standard vaporization temperature. 
   The present invention is conducted in a continuous fashion, such that a stream of the vapor precursor  42 ,  140  and the barrier gas  20 ,  154  mixture is continually produced having a uniform, high concentration of vapor precursor  42 ,  140 . In each of the above-described embodiments, the stream is caused to flow from the vaporization chamber  26 ,  138  through an outlet  168 ,  170  to a conduit (not shown) to the surface of the hot substrate (not shown) by means of pressure generated by the vaporization of the liquid precursor  40 ,  148  injected through the inlet  44 ,  166  and by the introduction of the pressurized barrier gas  20 ,  140  into the vaporization chamber  26 ,  138 . 
   Most coating precursors, when vaporized, are extremely flammable under oxidizing conditions, and therefore can only be conveyed to the reaction site in a barrier gas stream at a concentration of a few gas phase percent. Higher concentrations of coating precursor vapor will ignite when contacted with the surface of the hot substrate in an oxidizing atmosphere. Therefore, the coating operation must be conducted utilizing a vaporized coating precursor stream having a concentration below the flammability limit for that particular coating precursor. 
   Coatings may be deposited onto the surface of a hot glass substrate by chemical vapor deposition (not shown). This process is typically conducted during the manufacture of glass by the float glass process, and may occur in the float bath where the glass ribbon is typically at a temperature in the range of about 1100° F. to about 1250° F., the lehr (glass temperatures of about 750° F. to about 1050° F.), or in the transition zone between the bath and the lehr (glass temperatures of about 1025° F. to about 1100° F.). Coating precursors are vaporized and conveyed to a point at or near the surface of the advancing glass ribbon. In the presence of oxygen, the coating precursors pyrolytically decompose to form an oxide coating on the surface of the glass. However, the invention is not limited to the deposition of oxide coatings, but can also be used when depositing non-oxide coatings such as silicon or transition metal nitrides. In addition, the invention can be used for chemical vapor deposition on any substrate, and is not limited to deposition on glass. 
   It must be noted that the process conditions are not sharply critical for the successful preparation of vaporized reactants according to the present invention. The process conditions described hereinabove are generally disclosed in terms which are conventional to the practice of this invention. Occasionally, however, the process conditions as described may not be precisely applicable for each compound included within the disclosed scope. Those compounds for which this occurs will be readily recognizable by those ordinarily skilled in the art. In such cases, the process may be successfully performed by conventional modifications known to those ordinarily skilled in the art, e.g., increasing or decreasing temperature conditions, varying the rates of introduction of the coating precursor or blend gas, changing to alternative CVD reactants or barrier gases, routine modifications of the vaporization process conditions, etc. 
   In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.