5924-5929 Users Guid..
Contents
1. The correction for the pressure difference Except for a few triple points the values of temperature assigned to the defin ing fixed points by ITS 90 correspond to the temperatures at the standard atmo spheric pressure 101 325 kPa The actual pressure in a cell may be not exactly the standard value During the course of manufacture of a fixed point cell it is easier for a glassblower to seal the cell if the pressure in the cell is a slightly lower than the room pressure The actual pressure in the cell exactly at the fixed point was measured at Hart This information is provided on the Re port of Test enabling the used to correct for the difference in pressure During measurement at a fixed point the sensor of a SPRT is usually placed at a height which is h meters lower than the surface of the matter used for the fixed point and where the pressure is higher than that at the surface due to the static head ITS 90 gives all of the necessary coefficients for the calculation of the correc tion caused by the pressure difference which are summarized in following table Table 7 Coefficients for the pressure difference of some defining fixed points Assigned Value of Temperature Variation with Equilibrium Temperature with Pressure p depth Approximate T k dT dp k dT dh Substance Kelvin K 10 5 mK Pa mK m dW dt 1 K Argon T 83 8058 25 3 3 0 004342 Mercury T 234 3156 5 4 7 1 0 004037 Water T 273 16 7 5 0 72. Hart Scientific 5924 5929 Metal Freeze Point Cell User s Guide Rev 5A2101 Fluke Corporation Hart Scientific Division 799 E Utah Valley Drive American Fork UT 84003 9775 USA Phone 1 801 763 1600 Telefax 1 801 763 1010 Email support hartscientific com www hartscientific com Subject to change without notice Copyright 2005 Printed in USA Rev 5A2101 Table of Contents 1 Before YouStart 1 1 1 2 1 3 Symbols Used o cu ee we ewe ba Ce eet wee rte Safety Information su go a ae aS oe de ban pee 1 2 1 WPT 9S sg s ee RG gs are een EN eo i er tae ande oe EY ee 1 2 2 Cautions ce wie ok BS Bae ee Ae SR EE sise Authorized Service Centers 2 Introduction 3 Specifications lt gt se 6 ss sacs 6e 8 0 6e 6 6 66 6 6 Description s o gt die see sue r ee etes le 6 8 5 Care of Your Metal Freezing Point Cell 11 5 1 5 2 General Information s s 4 ee su munis das dass Devitrification of Quartz Glass 6 Realization of the Freezing Point 13 6 1 Unpackimp rs sx 3 a6 d s BA mea ss bia eee 3 6 2 Assembly Guide 6 3 Background Information 6 4 Maintaining the cell with argon 6 5 Vertical temperature gradient and controller accuracy adjustment 6 5 1 Vertical temper
3. OVERVOLTAGE CATEGORY II is energy consuming equipment to be supplied from the fixed installation Examples include household office and laboratory appliances C TIC Australian EMC Mark i The European Waste Electrical and Electronic Equipment WEEE Directive 2002 96 EC mark 1 2 Safety Information Use this instrument only as specified in this manual Otherwise the protection provided by the instrument may be impaired The following definitions apply to the terms Warning and Caution e Warning identifies conditions and actions that may pose hazards to the user e Caution identifies conditions and actions that may damage the instru ment being used 1 2 1 A Warnings To avoid personal injury follow these guidelines e DO NOT use this instrument to measure the temperature of any hazardous live component e DO NOT use this unit for any application other than calibration work e DO NOT use this unit in environments other than those listed in the user s manual e Use of this instrument at high temperatures for extended periods of time can cause the handle to become hot e Follow all safety guidelines listed in the user s manual e Calibration Equipment should only be used by Trained Personnel 1 2 2 Cautions To avoid possible damage to the instrument follow these guidelines e DO NOT remove the label from the handle This cautions the user con cerning the delicate nature o
4. 6 5 6 5 1 6 5 2 Vertical temperature gradient and controller accuracy adjustment Vertical temperature gradient adjustment The vertical temperature gradient has to meet the requirement before the sam ple is to be melted Otherwise the cell may be broken Therefore the vertical temperature gradient should be measured after the cell is installed every time and checked later at least every six months 9114 and 9116 furnaces are three zone furnaces and their temperature gradient could be adjusted through the top zone and the bottom zone heater The 9115 furnace is a heat pipe fur nace The temperature vertical gradient is always very good and it is not neces sary to adjust the gradient if the heat pipe works properly Actually the temperature gradient of the 9115 furnace cannot be adjusted Vertical temperature gradient test method Set the furnace temperature 5 C below the melting point of the sample For ex ample the melting point temperature of Zinc is 419 527 C the furnace temper ature should be set to 414 5 C Maintain the temperature for at least 4 hours stabilizing after the display temperature of the furnace reaches the set point temperature The SPRT is moved up 180 mm from the bottom of the thermom eter well and then back to the bottom The SPRT was moved in 50 mm incre ments and measurements taken at each depth After every move and before each measurement a two minute stabilization period was allowed The v
5. than ten hours The changes in temperature in the first half of the plateau are usually within 0 2 to 0 3 mK A typical freezing curve is shown in Figure 7 on page 21 Realization of the freezing point of In 1 Start pumping by using a mechanical vacuum pump When the pressure reaches approximately 1e 2 torr open the vacuum valve slowly If the pressure reaches approximately 1e 2 again it might take about 30 min utes it indicates all connections and sealing are in good condition If not check all connections and sealing one by one 2 Turn on the high vacuum system diffusion pump or molecular pump and open high vacuum valve to pump cell The vacuum should be at 1e 5 torr or lower 3 Insert an SPRT into the reentrant well of the cell to monitor the tempera ture of the cell 4 Make sure the vertical temperature gradient of the furnace with the cell is good enough The furnace vertical temperature gradient should be 25 5924 5929 Metal Freeze Point Cell User s Guide 26 6 6 2 10 11 12 13 checked and adjusted if necessary at first operation and therefore every 6 months please refer to the 9114 manual Turn on the power to the furnace and raise the temperature to 162 C with a rate of 3 C min while pumping continually During this period rinse the cell with pure argon 99 999 two or three times As soon as the indium is melted change furnace temperature down to 2 C higher than freezing point
6. Cell User s Guide 5 Turn on the power to the furnace and raise the temperature to 600 C with a rate of 3 C min while pumping continually 6 The furnace should be maintained at 600 C for 2 hours while pumping continually 7 Rinse the cell with pure argon 99 999 two or three times Fill the ar gon to the cell with a pressure of 94 kPa 8 Raise furnace temperature to 665 5 C with a rate of 3 C A WARNING DO NOT pump the cell for more than 10 seconds 9 As soon as the temperature of the monitor SPRT reach 660 323 C melt ing point pump the cell for 10 seconds using mechanical pump Fill pure argon to the cell Adjust the pressure close to the standard atmo sphere and record the actual pressure in order to make the correction for the pressure differences as shown in Chapter 7 10 As soon as the aluminum is melted change furnace temperature down to 2 C higher than freezing point temperature of aluminum 662 5 C 11 Allow the temperature to stabilize for two hours 12 Set furnace temperature 2 C below freezing point temperature 658 C with a decrease rate of 0 1 C min 13 When recalescence is observed the SPRT is removed and a room tem perature quartz rod is inserted for 1 min or quartz tube for 2 min creates double freeze 14 Set furnace 1 C below freezing point temperature 659 4 C 15 The first SPRT check SPRT to be calibrated is inserted into reentrant well and measurements are made af
7. Pa and k 1 6 mK m The average immersion depth is 0 17 m for most of standard platinum resistance thermometers Therefore use Equation 1 to calcu late At Substituting values into Equation 1 5 80 817Pa 101 325Pa 010 K on 144mK 0 27mK Pa m Consequently At 1164mK Hence the actual temperature of a sensor of a SPRT at the point of total immer sion during a freezing plateau in the cell is calculated using Equation 2 Equation 2 Calculation of the Actual Temperature t4 t t Ar Therefore t 660 323 C 0 001164 C 660 32184 C where t is the defining fixed point temperature i e 660 323 C for the freezing point of aluminum The resistance ratio W for the particular cell exactly at the freezing point of aluminum can be calculated using the following equation The value for dW dt is taken from Table 7 Equation Calculation of W for the exact defining fixed point temperature 7 The correction for the pressure difference dw W WD AN r Substituting values 3 37600860 1164 x 10 3 204971 x 103 Thus the W for the cell is W 3 37601233 37
8. The furnace vertical temperature gradient should be checked at first operation and therefore every 6 months please refer to the 9116 manual Turn on the power to the furnace and raise the temperature to 850 C with a rate of 3 C min while pumping continually The furnace should be maintained at 850 C for 2 hours while pumping continually Rinse the cell with pure argon 99 999 two or three times Fill the ar gon to the cell with a pressure of 84 kPa Raise the temperature of the furnace to 1091 C with ramp rates as the follows 3 C min below 1000 C 2 C min below 1070 C and 1 C min below 1091 C WARNING DO NOT pump the cell for more than 10 seconds 9 10 11 As soon as the temperature of the monitor TC reach 1084 62 C melting point pump the cell for 10 seconds using mechanical pump Fill pure argon to the cell Adjust the pressure close to the standard atmosphere and record the actual pressure in order to make the correction for the pressure differences as shown in Chapter 7 As soon as the copper is melted change furnace temperature down to 2 C higher than freezing point temperature of copper 1086 6 C Allow the temperature to stabilize for two hours 6 Realization of the Freezing Point SPRT Care At High Temperatures 12 13 14 15 16 17 Set furnace temperature 2 C below freezing point temperature 1082 6 C with a decrease rate of 0 1 C min When recalescence is
9. differences as shown in Chapter 7 Stabilize the temperature for two hours Set furnace temperature 3 C below freezing point temperature 228 C with a decrease rate of 0 1 C min When the temperature indicated by a thermometer immersed in the tin sample reaches the freezing point using the Model 9114 furnace intro duce a cold gas flow upward around the outer surface of the cell until recalescence Cold gas flow means compressed air at an approximate rate of 5 20 liter min 0 2 0 7 CFM and roughly 200 kPa 29 psia When recalescence is observed shut off the cold gas flow The SPRT is removed and two room temperature quartz rods are inserted one by one for 2 min each creates double freeze Set furnace 1 C below freezing point temperature 230 9 C The first SPRT check SPRT to be calibrated is inserted into reentrant well and measurements are made after the cell and SPRT are in the equi librium The first SPRT is at room temperature at the time of insertion The furnace temperature is kept at a stable temperature of 1 C below the freezing point After all SPRTs are measured set the furnace temperature at 20 C with a rate of 2 C min The cell should be pumped for 10 min in the second day At that time the furnace temperature should close to room temperature Fill pure ar gon to a pressure that is slightly higher than local atmosphere pressure Close all valves Turn the furnace power off Realizati
10. metal freezing points of the ITS 90 pressure constants and resistance ratios Table 3 Some subranges of the ITS 90 and freezing points required for CalibratiOites ao 6 Saw sie hoet ESS te RS bises Seas Table 4 The specification of metal freezing point cells Table 5 Summary of the Ist Cryoscopic Constants and the Estimated Effects of Impurities o ers sim un Gone Roe a UE re ce Sow Table 6 The furnaces for fixed points and their temperature uniformity Table 7 Coefficients for the pressure difference of some defining fixed points iii 1 Before You Start Symbols Used 1 1 Before You Start Symbols Used Table 1 lists the International Electrical Symbols Some or all of these symbols may be used on the instrument or in this manual Table 1 International Electrical Symbols Symbol Description NV AC Alternating Current ING AC DC Battery M MA CE Complies with European Union Directives DC Double Insulated Electric Shock Fuse PE Ground Hot Surface Burn Hazard Read the User s Manual Important Information Off O gt Ol eH On 5924 5929 Metal Freeze Point Cell User s Guide Symbol Description Canadian Standards Association US OVERVOLTAGE Installation CATEGORY II Pollution Degree 2 per IEC1010 1 re CATI fers to the level of Impulse Withstand Voltage protection provided Equipment of
11. observed the TC is removed and a room tempera ture quartz tube is inserted for 1 min creates double freeze Set furnace 1 C below freezing point temperature 1083 6 C The first thermocouple to be calibrated is inserted into reentrant well and measurements are made after the cell and TC are in the equilibrium The first TC is at room temperature at the time of insertion The furnace tem perature is kept at a stable temperature of 1 C below the freezing point After all thermocouples are measured set the furnace temperature at 20 C with a rate of 2 C min The cell should be pumped for 10 min in the second day At that time the furnace temperature should close to room temperature Fill pure ar gon to a pressure that is slightly higher than local atmosphere pressure Close all valves Turn the furnace power off SPRT Care At High Temperatures Each SPRT calibrated at temperatures above 500 C is subjected to quenched in vacancy defect effect when the SPRT is removed from the furnace This quenched in lattice vacancy defect effect must be removed before calibration at the triple point of water Therefore when the SPRT is removed from the cell place it in an auxiliary furnace set at the same temperature as the fixed point Slowly cool the SPRT at a rate of roughly 100 C hour above 500 C Once the SPRT has reached 500 C it may be removed directly to room temperature 33 7 The correction for the pressure difference
12. of silver Model 9115 furnace heat pipe 0 05 C The freezing point of copper Model 9116 furnace single zone 0 2 C The cell basket should be put into the furnace before placing the cell in the cell basket The cell containment vessel basket for the Model 9114 furnace is shown in Figure 6 A nickel container is used to support the freezing point cell for Model 9115 Figure 4 and an inconel container is used for the Model 9116 furnace Fiber ceramic insulation minimum of 50 mm 2 in is placed in the bottom of the cell basket to protect the cell Maintaining the cell with argon Connect the cell to a pumping and filling system Check all of the connections to make sure they are in good condition Check the seven screws on the cap to see if they are tight enough and tighten a little if necessary Start pumping by using a mechanical vacuum pump When the pressure reaches approximately le 2 torr open the vacuum valve slowly If the pressure reaches approximately le 2 again it might take about 30 minutes it indicates all connections and sealing are in good condition If not check all connections and sealing one by one Pump the cell using a diffusion pump or molecular pump for at least 4 hours Rinse the cell with 99 999 pure argon three or four times and fill the cell with pure argon to a pressure that is slight higher than local atmosphere pressure Close all valves 23 5924 5929 Metal Freeze Point Cell User s Guide 24
13. point cell In order to get the highest possible accuracy a general understanding of the freezing pro cess of an ideal pure metal is helpful Unpacking Since it is difficult to hand carry or deliver an assembled 592X fixed point cell the 592X fixed point cell must be delivered as a kit The kit is comprised of the following parts 1 Crucible assembly sealed in a Pyrex vessel in dry pure argon atmosphere 2 High purity graphite disks 6 pieces sealed in a Pyrex vessel in dry pure argon atmosphere same Pyrex vessel as for crucible assembly 3 Pure fused silica quartz glass wool disks in a Pyrex tube 4 Fused silica quartz glass outer shell 1 piece 5 Fused silica quartz glass reentrant well 1 piece 6 A clean Pyrex tube or rod used as tool and will not be assembled into the cell 7 Extra clean ash less filter papers used during assembling Stainless steel SS cap assembly 1 set including the following parts see fig 2 in details all of the parts were assembled loosely and packed in a polyethylene bag e SS top cover 1 piece e SS well clamp 1 piece e SS cover clamp ring piece e Silicone O ring 1 862 ID x 103w 1 piece e Silicone O ring 424 ID x 103w 1 piece e Silicone seal washer 64 mm 50 6 mm x 5 mm 1 piece e High vacuum bellow valve NUPRO SS 4H 1 piece e SS valve support bracket piece e Screw 8 32 x 1 SKTHD CAP 4 pieces e Screw 4 40 x 4 SKTHD CAP SST 3 pieces e Screw 8 32
14. temperature of indium 158 6 C Rinse the cell with pure argon 99 999 two or three times Fill the argon to the cell Adjust the pressure close to the standard atmosphere and record the actual pressure in order to make the correction for the pressure differ ences as shown in Chapter 7 Stabilize the temperature for two hours Set furnace temperature 3 C below freezing point temperature 153 6 C with a decrease rate of 0 1 C min When recalescence is observed the SPRT is removed and a room tem perature quartz rod is inserted for 1 min or quartz tube for 2 min creates double freeze Set furnace 1 C below freezing point temperature 155 6 C The first SPRT check SPRT to be calibrated is inserted into reentrant well and measurements are made after the cell and SPRT are in the equi librium The first SPRT is at room temperature at the time of insertion The furnace temperature is kept at a stable temperature of 1 C below the freezing point After all SPRTs are measured set the furnace temperature at 20 C with a rate of 2 C min The cell should be pumped for 10 min in the second day At that time the furnace temperature should close to room temperature Fill pure ar gon to a pressure that is slightly higher than local atmosphere pressure Close all valves Turn the furnace power off Realization of the freezing point of Sn 1 Start pumping by using a mechanical vacuum pump When the pressure reaches appr
15. the furnace to a temperature of 5 C to 6 C above the melting point with a ramp of 0 5 C min Record the emf E Cu of the thermocouple during the melt ing plateau After the copper is melted and then decrease the furnace to a tem perature about 2 C above the freezing point maintain the furnace at this temperature for at least four hours or over night Check the accuracy of the fur nace set temperature When the temperature is stable at this temperature record the emf E1 The actual temperature t can be calculated as the following equation t 1084 62 C E1 E Cu dE dt dE dt is 13 6 uV C for a Type R thermocouple and 11 8 uV C for a Type S thermocouple Compare the calculated actual temperature and the furnace set temperature it is easy to calculate the correction for the furnace set tempera ture For example the furnace set temperature is 1085 6 C and the calculated actual temperature is 1086 0 C the correction is 0 4 C It is suggested that this be performed each time Procedure for realizing the freeze In Zn Al Ag and Cu fixed points WARNING Due to different vapor pressure at the freezing points the pumping and filling procedures are different for different fixed points This is the recommended procedure to realize the freezing point of 592X fixed point cells Other procedures are sometimes employed in industry These proce dures provide a very stable long freezing plateau that typically lasts for more
16. x 5 16 PPHD 2 pieces 13 5924 5929 Metal Freeze Point Cell User s Guide 6 2 Assembly Guide 1 Assembly should be performed in a clean surrounding It is suggested to put clean paper on a working table in a very clean room Wear new clean gloves during assembling The crucible assembly should only be touched by ash less filter paper provided Carefully break the top of the Pyrex vessel containing the crucible as sembly and graphite disks with a clean metal tool Take the graphite disks out of the Pyrex vessel and put them on a piece of ash less filter pa per in a clean place Because the crucible assembly was sealed in a pure and dry argon atmosphere to avoid possible contamination break the Py rex vessel only when you have made good preparation Complete the en tire assembling work in as short period as possible to avoid contamination and oxidation to pure metal Keep the cell fused silica outer shell later we will call it as outer shell at an angle about 10 to the horizontal direction let the crucible assembly slide slowly and gently to the bottom of the outer shell Use a piece of ash less filter paper to hold the crucible assembly during the process Put one piece of graphite disk on the top of the crucible assembly Carefully take pure fused silica wool disks from Pyrex tube and put them into the outer shell using the Pyrex tube as a tool Put more pure fused silica wool disks into the outer shell until the heigh
17. 118502 SINGAPORE Phone 65 6799 5588 Telefax 65 6799 5588 E mail antng singa fluke com When contacting these Service Centers for support please have the following information available e Model Number e Serial Number e Complete description of the problem 2 Introduction Introduction The International Temperature Scale of 1990 ITS 90 is based on a series of defining fixed points At temperatures above 273 16 K most of the fixed points are the freezing points of specified pure metals Pure metals melt and freeze at a unique temperature through a process involving the absorption or liberation of the latent heat of fusion A metal freezing point is the phase equilibrium be tween the liquid phase and solid phase of a pure metal at a pressure of one stan dard atmospheric pressure 101 325 Pa The freezing points of indium tin zinc aluminum silver gold and copper are the defining fixed points of the ITS 90 The temperature values of these freezing points assigned by the ITS 90 the pressure effect constants and the resistance ratios are listed in Table 2 Table 2 The defining metal freezing points of the ITS 90 pressure constants and resistance ratios Pressure Effect of Fixed Points ASSIGNED TEMPERATURE dt dP dt dh dW Jdt FIXED POINT Ta K teo C 10 K Pa t 10 K m W Too x 0 001 FP In 429 7485 156 5985 4 9 3 3 160980185 3 801024 FP Sn 505 078 231 928 3 3 2 2 1 89279768 3 712721 FP Zn 69
18. 2 677 419 527 43 2 7 2 56891730 3 495367 FP Al 933 473 660 323 7 0 1 6 3 37600860 3 204971 FP Ag 1234 98 961 78 6 0 5 4 4 28642053 2 840862 FP Au 1337 33 1064 18 6 1 10 FP Cu 1357 77 1084 62 33 26 Equivalent to millikelvins per standard atmosphere All of these fixed points are intrinsic temperature standards according to the definition of the ITS 90 In certain conditions these freezing points are highly reproducible obtaining almost the same temperature wherever and whenever a freezing point is realized The difference among different realizations of a freezing point might be well within 1 0 mK for the freezing points of indium tin and zinc within a few millikelven for the freezing points of aluminum and silver For your convenience Hart has developed several different designs of fixed point cells for the realization of the freezing points Hart has open fixed point cells for those who desire work with traditional fixed points Addi tionally Hart has developed sealed cells in several configurations which has made it easy to realize these fixed points The 5900 series and 5910 series of fixed point cells are completely sealed cells The 5920 series of cells are long cells with stainless steel caps and ports for pumping and filling argon gas 5924 5929 Metal Freeze Point Cell User s Guide Figure 1 Metal Freezing Point Cell These freezing points are indispensable for the calibration of a standard plati num resistance ther
19. 3 0 003989 Gallium M 302 9146 2 0 1 2 0 003952 Indium F 429 7485 4 9 3 3 0 003801 Tin F 505 078 3 3 2 2 0 003713 Zinc F 692 677 4 3 2 7 0 003495 Aluminum F 933 473 7 0 1 6 0 003205 Silver F 1234 93 6 0 5 4 0 002841 Gold F 1337 33 6 1 10 Copper F 1357 77 3 3 2 6 The correction of temperature caused by the difference in pressure can be cal culated by using the following equation Equation Pressure Dependent Temperature Correction At P P xk hxk Where P the actual pressure of argon in the cell exactly at the fixed point temperature 35 5924 5929 Metal Freeze Point Cell User s Guide 36 Po the standard atmospheric pressure i e 101 325 Pa k dT dp k dT dh and h the immersion depth of the midpoint of the sensor of a SPRT into the mat ter used for the fixed point The immersion depth of the midpoint of a SPRT sensor in Hart metal freezing point cell is approximately 0 18 m the distance from the bottom of the central well to the surface of liquid metal is about 0 195 m The actual pressure of the argon at the freezing point in the cell p is provided in the Report of Test The temperature correction At can be calculated using Equation 1 Example The pressure of argon at the freezing point in the aluminum freezing point cell S N 5907 5 AL004 is 80 817 Pa as given in the Report of Test kl and k2 for the freezing point of aluminum can be found in Table 5 k 7 0 10 mK
20. 54 0 6552549 0 6552544 0 6552539 0 6552534 rate of 2 C min The cell should be pumped for 10 min in the second day At that time the furnace temperature should close to room temperature Fill pure ar gon to a pressure that is slightly higher than local atmosphere pressure Close all valves Turn the furnace power off 10 8 10 8 10 8 10 8 10 8 10 9 10 9 10 9 10 9 10 9 10 00 13 00 16 00 19 00 22 00 1 00 4 00 7 00 10 00 13 00 Date and time Figure 9 A typical freezing curve for the Zinc Cell Realization of the freezing point of Al 1 Start pumping by using a mechanical vacuum pump When the pressure reaches approximately le 2 torr open the vacuum valve slowly If the pressure reaches approximately 1e 2 again it might take about 30 min utes it indicates all connections and sealing are in good condition If not check all connections and sealing one by one Turn on the high vacuum system diffusion pump or molecular pump and open high vacuum valve to pump cell The vacuum should be at 1e 5 torr or lower Insert an SPRT into the reentrant well of the cell to monitor the tempera ture of the cell Make sure the vertical temperature gradient of the furnace with the cell is good enough The furnace vertical temperature gradient should be checked and adjusted if necessary at first operation and therefore every 6 months please refer to the 9114 manual 29 5924 5929 Metal Freeze Point
21. OM END ZONE Bottom Zone Water Cooling Heater Coils Supercooling Gas Supply Argon Figure 3 9114 Furnace Interior with Freeze Point Cell Cross Sectional View 16 6 Realization of the Freezing Point Background Information Entrant Well Pa Purge Gas Connection Cooling Water Ports Top Support Block Retaining Plate Cooling Flange j Top Cover Cutout Thermocouple Cooling Coils Heating Element Control and Cutout Thermocouple Metal Freeze Point Cell Heat Pipe Ceramic Fiber Insulation Air Gap Circulating Air Bottom Support Block Figure 4 9115 Furnace Interior with Freeze Point Cell Cross Sectional View 17 5924 5929 Metal Freeze Point Cell User s Guide Entrant Well Cooling Water Ports 4 Purge Gas Connection Top Support Block Retaining Plate Top Cover Cutout Thermocouple Cooling Coils Heating Element Control and Cutout Thermocouple Metal Freeze Point Cell Heater Liner Figure 5 9116 Furnace Interior View 18 Cermic Fiber Insulation Air Gap Circulating Air 6 Realization of the Freezing Point Background Information and freezing equilibrium points are usually slightly lower The
22. ature gradient adjustment 6 5 2 Controller display accuracy adjustment 6 6 Procedure for realizing the freeze In Zn Al Ag and Cu fixed points 25 6 6 1 Realization of the freezing point of In 6 6 2 Realization of the freezing point ofSn 6 6 3 Realization of the freezing point of Zn 6 6 4 Realization of the freezing point of A1 6 6 5 Realization of the freezing point of Ag 6 6 6 Realization of the freezing point of Cu 6 7 SPRT Care At High Temperatures 13 7 The correction for the pressure difference 35 Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Metal Freezing Point Cell The Hart open metal freezing point cell 9114 Furnace Interior with Freeze Point Cell Cross Sectional View 9115 Furnace Interior with Freeze Point Cell Cross Sectional View 9116 Furnace Interior View The metal freezing point cell in the cell containment vessel basket Freezing curve comparison of one cell Two liquid solid interfaces in the cell A typical freezing curve for the Zinc Cell Tables Table 1 International Electrical Symbols Table 2 The defining
23. d be checked at first operation and therefore every 6 months please refer to the 9115 manual Turn on the power to the furnace and raise the temperature to 800 C with a rate of 3 C min while pumping continually The furnace should be maintained at 800 C for 2 hours while pumping continually Rinse the cell with pure argon 99 999 two or three times Fill the ar gon to the cell with a pressure of 90 kPa Raise furnace temperature to 966 C with a rate of 3 C WARNING DO NOT pump the cell for more than 10 seconds 9 10 11 12 13 14 15 As soon as the temperature of the monitor SPRT reach 961 78 C melt ing point pump the cell for 10 seconds using mechanical pump Fill pure argon to the cell Adjust the pressure close to the standard atmo sphere and record the actual pressure in order to make the correction for the pressure differences as shown in Chapter 7 As soon as the silver is melted change furnace temperature down to 2 C higher than freezing point temperature of silver 963 8 C Allow the temperature to stabilize for two hours Set furnace temperature 2 C below freezing point temperature 959 8 C with a decrease rate of 0 1 C min When recalescence is observed the SPRT is removed and a room tem perature quartz tube is inserted for 2 min creates double freeze Set furnace 1 C below freezing point temperature 960 8 C The first SPRT check SPRT to be calibrated is i
24. e monitor SPRT reach 419 527 C melt ing point pump the cell for 10 seconds using mechanical pump Fill pure argon to the cell Adjust the pressure close to the standard atmo sphere and record the actual pressure in order to make the correction for the pressure differences as shown in Chapter 7 As soon as the zinc is melted change furnace temperature down to 2 C higher than freezing point temperature of zinc 421 5 C Stabilize the temperature for two hours Set furnace temperature 2 C below freezing point temperature 417 5 C with a decrease rate of 0 1 C min When recalescence is observed the SPRT is removed and a room tem perature quartz rod is inserted for 1 min or quartz tube for 2 min creates double freeze Set furnace 1 C below freezing point temperature 418 5 C The first SPRT check SPRT to be calibrated is inserted into reentrant well and measurements are made after the cell and SPRT are in the equi librium The first SPRT is at room temperature at the time of insertion The furnace temperature is kept at a stable temperature of 1 C below the freezing point 6 Realization of the Freezing Point Procedure for realizing the freeze In Zn Al Ag and Cu fixed points 6 6 4 16 After all SPRTs are measured set the furnace temperature at 20 C with a 17 F18 Bridge reading Rt Rs 0 6552529 T T T 0 6552574 0 6552569 JAANA E a Motte 0 5 mK 0 6552564 0 6552559 mes CN 0 65525
25. er quantity of metal See Table 3 for detail with a purity of 99 9999 is melted into a graphite crucible with a graphite lid and re entrant well The impurity in the graphite is less than 5 PPM All of the graphite parts are subjected to a high temperature high vacuum treatment before loading the metal sample It is important to avoid any possible contamination to the surface of the graphite parts during the manufacturing process A graphite disk sits on the crucible The assembled graphite crucible with the high purity metal is then enclosed in a long quartz cell Pure silica wool insulation is interspersed between graphite disks to act as a thermal barrier The cell is sealed with a spe cially designed stainless steel cap with a port and vacuum valve The cell is connected to a pumping and filling system and then drawn down to a proper pressure at a temperature near the freezing point for several days During this period the cell is purged with high purity argon repeatedly to remove any ab sorption gas on the surface of all parts in the cell Finally the cell is filled with 99 999 pure argon at a pressure close to 101 325 Pa at room temperature and the vacuum valve closed In providing the highest quality fixed point cells on the market Hart s experts carefully eliminate possible sources of errors For ex ample sand blasting the outer surface of the central re entrant quartz well of the sealed cell decreases the radiation losses along the well
26. ertical temperature requirements are listed in Table 6 on page 23 If the furnace does not meet the requirement the vertical temperature gradient should be adjusted through the top and bottom heater model 9114 and 9116 For 592X fixed point cells you have to combine the process of vertical temper ature gradient measurement and the process of pumping the cell together The vacuum pump process is described in 6 4 Controller display accuracy adjustment The absolute accuracy of the controller display is not so important However the accuracy should be checked to know the offset using a calibrated SPRT for 9114 and 9115 or thermocouple for 9116 The offset should be considered or corrected during the realization of fixed points The controller accuracy should be corrected after vertical temperature gradient is adjusted The accuracy might change after temperature gradient is adjusted The controller accuracy should be checked after the sample fully melted in every realization of fixed point Please refer the 9114 9115 9116 furnace manual for the accuracy adjustment method A calibrated SPRT or thermocouple should be used to measure the controller accuracy For the realization of cooper cell due to the thermocouple accuracy is usually not good enough for the realization please refer the following method 6 Realization of the Freezing Point Procedure for realizing the freeze In Zn Al Ag and Cu fixed points 6 6 6 6 1 Raise
27. f the instrument 1 Before You Start Authorized Service Centers 1 3 e DO NOT drop or bang the probe in any way This will cause damage to the probe internally and affect its calibration e Read Section entitled PRT Care and Handling Guidelines before re moving the PRT from the shipping box or case Incorrect handling can damage the PRT and void the warranty e Keep the shipping container in case it is necessary to ship the PRT Incor rect packaging of the PRT for shipment can cause irreparable damage Authorized Service Centers Please contact one of the following authorized Service Centers to coordinate service on your Hart product Fluke Corporation Hart Scientific Division 799 E Utah Valley Drive American Fork UT 84003 9775 USA Phone 1 801 763 1600 Telefax 1 801 763 1010 E mail support hartscientific com Fluke Nederland B V Customer Support Services Science Park Eindhoven 5108 5692 EC Son NETHERLANDS Phone 31 402 675300 Telefax 31 402 675321 E mail ServiceDesk fluke nl Fluke Int l Corporation Service Center Instrimpex Room 2301 Sciteck Tower 22 Jianguomenwai Dajie Chao Yang District Beijing 100004 PRC CHINA 5924 5929 Metal Freeze Point Cell User s Guide Phone 86 10 6 5 12 3436 Telefax 86 10 6 5 12 3437 E mail xingye han fluke com cn Fluke South East Asia Pte Ltd Fluke ASEAN Regional Office Service Center 60 Alexandra Terrace 03 16 The Comtech Lobby D
28. freezing plateau of an ideal pure metal is conceptually flat The only exception is during the supercool Impurities in the metal generally introduce a slightly negative slope to the plateau Most of the different types of impurities will cause a drop in the freezing plateau e g gallium impurities in tin will cause a drop in the freezing plateau A few of the types of impurities can cause an increase in the plateau e g gold impurities in silver will cause the freezing plateau to increase An ex tremely high purity metal 99 9999 or higher behaves very closely to an ideal pure metal Figure 7 shows the difference between a freeze of an ideal pure metal and a high purity metal The approximate effect of the impurity on the equilibrium point can be calculated using the first cryoscopic constant This calculation is discussed in the Guidelines for Realizing the International Tem perature Scale of 1990 ITS 90 For general uncertainty comparisons the first cryoscopic constant the metal purity requirement and the difference in the liquidus point are outlined in Table 5 In a modern temperature standard labora tory using a SPRT a temperature change as low as 0 01 mK 0 00001 C can be detected Therefore the best technique for realizing the freezing point with a real sample is one that measures a temperature nearest to the freezing point of the ideal pure metal The beginning of the freezing curve of a high purity metal is the closest temperature t
29. its most stable state If the quartz glass is kept extremely clean and free of contamination devitrification will occur only at high temperatures The process occurs more rapidly at lower temperatures when the quartz glass has become contaminated by alkaline metals Na K Mg and Ca The alkalis found in normal tap water can cause the process to start There is conflicting opinion among the experts as to whether the process can be stopped Some say that once the process starts it does not stop Others indicate that once the alkali is removed the process will stop Removal of the devitrification is not practical as it requires drastic measures and is potentially dangerous to the instrument and or the user Devitrification starts with a dulling or opacity of the quartz glass It develops into a rough and crumbling surface Devitrification ultimately weakens the quartz glass until it breaks or is otherwise no longer useful The best cure for contamination and devitrification is prevention Being aware of the causes and signs of contamination can help the user take the steps neces sary to control contamination of the cell Keep your cell clean and avoid con tact with bare hands tap water or contaminated SPRTs 11 6 Realization of the Freezing Point Unpacking 6 1 Realization of the Freezing Point As was mentioned in Section 1 Introduction it is not difficult to realize a freezing point by using the Hart Scientific metal freezing
30. mometer SPRT Different subranges require different sets of freezing points as summarized in Table 3 Table 3 Some subranges of the ITS 90 and freezing points required for calibration SUBRANGE FREEZING POINTS REQUIRED 0 C 961 78 C 0 C 660 323 C 0 C 419 527 C 0 C 231 928 C 0 C 156 5985 C FP Sn FP Zn FP Al and FP Ag FP Sn FP Zn and FP Al FP Sn and FP Zn FP In and FP Sn FP In 3 Specifications 3 Specifications Table 4 The specification of metal freezing point cells Model Number 5924 5925 5926 5927 5928 Contact 5929 Hart Fixed Point FP In FP Sn FP Zn FP Al FP Ag FP Au FP Cu Reproducibility mK 0 15 0 3 0 2 0 4 0 2 0 4 0 6 1 0 1 0 2 0 1 0 2 0 2 0 4 0 Expanded uncertainty mK 0 7 0 5 0 9 1 3 2 4 2 5 10 k 2 Metal Purity 99 9999 99 9999 99 9999 99 9999 99 9999 99 9999 99 9999 Quantity of metal kg 0 97 0 96 0 95 0 35 1 35 1 13 Outer diameter of the cell 50 50 50 50 50 50 50 mm Overall height of the cell 596 596 596 596 696 696 696 696 mm Inner diameter of the well 8 8 8 8 8 8 8 mm Total immersion deptht 195 195 195 195 195 195 195 mm The distance from the bottom of the re entrant well to the upper surface of the metal Other sizes of cells are available according to the customer s special requirement 4 Description Description A typical 592X Hart Scientific metal freezing point cell is shown in Figure 2 on page 15 A prop
31. nection Cooling d Valve Support Bracket Water Ports x Cooling Flange CL CE Reentrant Tube E 2 Graphite Crucible _ High Purity Metal Sample Figure 2 The Hart open metal freezing point cell 10 Connect the outlet of the vacuum valve to the pumping and filling sys tem according to the attached Swagelok tube fitting instructions 11 Open the vacuum valve and pump the cell using a mechanical vacuum pump The vacuum pressure should go down to about 0 01 torr If not check and tighten all of the screws Background Information Theoretically the melting and freezing temperatures for an ideal pure metal are identical However with the introduction of impurities in the metal the melting 15 5924 5929 Metal Freeze Point Cell User s Guide H Main Controller SPRT Equilibration fils Par Sensor Block Top Zone Heater lt Top Zone Controller lt TOP END ZONE set vow ue eur l lt lt Main Heater Differential TCs Freeze Point Cell gt lt PRIMARY ZONE H gt B Cell Support Container Differential TCs Thermal Block 3 zone subdivision Bottom Zone Controller I gt ID lt BOTT
32. nserted into reentrant well and measurements are made after the cell and SPRT are in the equi librium The first SPRT is at room temperature at the time of insertion The furnace temperature is kept at a stable temperature of 1 C below the freezing point 31 5924 5929 Metal Freeze Point Cell User s Guide 32 6 6 6 16 17 After all SPRTs are measured set the furnace temperature at 20 C with a rate of 2 C min The cell should be pumped for 10 min in the second day At that time the furnace temperature should close to room temperature Fill pure ar gon to a pressure that is slightly higher than local atmosphere pressure Close all valves Turn the furnace power off Realization of the freezing point of Cu 1 Start pumping by using a mechanical vacuum pump When the pressure reaches approximately le 2 torr open the vacuum valve slowly If the pressure reaches approximately 1e 2 again it might take about 30 min utes it indicates all connections and sealing are in good condition If not check all connections and sealing one by one Turn on the high vacuum system diffusion pump or molecular pump and open high vacuum valve to pump cell The vacuum should down to le 5 torr or lower Insert a type S or type R thermocouple TC into the reentrant well of the cell to monitor the temperature of the cell Make sure the vertical temperature gradient of the furnace with the cell is good enough 0 1 C over 170mm
33. o the ideal freezing point which can be obtained in a modern temperature standard laboratory A so called slow induced freezing technique was found to fit the purpose best The detail of the technique will be described a little later A very slow freeze allows enough time to calibrate a number of SPRTs in the beginning of a single freeze Table 5 Summary of the 1st Cryoscopic Constants and the Estimated Effects of Impurities 1st Cryoscopic Constant Deviation from Pure Substance Impurity Level Liquidus Point Indium 0 00732 K 99 99999 0 05 mK Tin 0 00329 K 99 9999 0 3 mK Zinc 0 00185 K 99 9999 0 5 mK Aluminum 0 00149 K 99 9999 0 7 mK Silver 0 000891 K 99 9999 1 1 mK Gold 0 000831 K 99 9999 1 2mK Copper 0 000857 K 99 9999 1 2 mK 19 5924 5929 Metal Freeze Point Cell User s Guide Fiber Ceramic Insulation Cell Containment Vessel or Basket Fiber Ceramic Paper to center cell in basket Metal Freeze Point Cell cell interior construction shown Fiber Ceramic Cushion Figure 6 The metal freezing point cell in the cell containment vessel basket 20 6 Realization of the Freezing Point Background Information 660 38 660 36 660 34 660 32 a a a a gt N w Temperature C 660 26 660 24 660 22 T r r T T T Time hours The
34. on of the freezing point of Zn ile Start pumping by using a mechanical vacuum pump When the pressure reaches approximately le 2 torr open the vacuum valve slowly If the pressure reaches approximately 1e 2 again it might take about 30 min 27 5924 5929 Metal Freeze Point Cell User s Guide utes it indicates all connections and sealing are in good condition If not check all connections and sealing one by one Turn on the high vacuum system diffusion pump or molecular pump and open high vacuum valve to pump cell The vacuum should down to le 5 torr or lower Insert an SPRT into the reentrant well of the cell to monitor the tempera ture of the cell Make sure the vertical temperature gradient of the furnace with the cell is good enough The furnace vertical temperature gradient should be checked and adjusted if necessary at first operation and therefore every 6 months please refer to the 9114 manual Turn on the power to the furnace and raise the temperature to 250 C with a rate of 3 C min while pumping continually The furnace should be maintained at 250 C for 2 hours while pumping continually Rinse the cell with pure argon 99 999 two or three times Fill the ar gon to the cell with a pressure of 80 kPa Raise furnace temperature to 425 C with a rate of 3 C A WARNING DO NOT pump the cell for more than 10 seconds 9 10 11 12 13 14 15 28 As soon as the temperature of th
35. oretical freezing curve of an ideal pure metal without supercool Freezing curve of an ideal pure metal with supercool a Freezing curve of a real high purity metal Figure 7 Freezing curve comparison of one cell The induced technique generates two liquid solid interfaces in the cell A con tinuous liquid solid interface that as nearly as is practical encloses the sensor of the SPRT being calibrated Another liquid solid interface is formed on the wall of the graphite crucible In such a situation the outer interface advances slowly as the liquid continues to solidify Ideally this generates a shell that con tinues to be of uniform thickness completely surrounding the liquid which it self surrounds the inner liquid solid interface that is adjacent to the thermometer well Figure 8 The inner interface is essentially static except when a specific heat extraction process takes place e g the insertion of a cool replacement thermometer It is the temperature of the inner liquid solid inter 21 5924 5929 Metal Freeze Point Cell User s Guide face that is measured by the thermometer Sometimes the inner liquid solid in terface is called the defining temperature interface lt _ _ Shell gt Graphite Crucible Liquid Sample Solid Sample Reentrant Tube Melting State Freezing State Figure 8 Two liquid solid interfaces in the cell It is extremely im
36. oximately 1e 2 torr open the vacuum valve slowly If the pressure reaches approximately 1e 2 again it might take about 30 min utes it indicates all connections and sealing are in good condition If not check all connections and sealing one by one Turn on the high vacuum system diffusion pump or molecular pump and open high vacuum valve to pump cell The vacuum should down to le 5 torr or lower Insert an SPRT into the reentrant well of the cell to monitor the tempera ture of the cell 6 Realization of the Freezing Point Procedure for realizing the freeze In Zn Al Ag and Cu fixed points 6 6 3 10 11 12 13 14 Make sure the vertical temperature gradient of the furnace with the cell is good enough The furnace vertical temperature gradient should be checked and adjusted if necessary at first operation and therefore every 6 months please refer to the 9114 manual Turn on the power to the furnace and raise the temperature to 238 C with a rate of 3 C min while pumping continually During this period rinse the cell with pure argon 99 999 two or three times As soon as the tin is melted change furnace temperature down to 2 C higher than freezing point temperature of tin 233 C Rinse the cell with pure argon 99 999 two or three times Fill the argon to the cell Ad just the pressure close to the standard atmosphere and record the actual pressure in order to make the correction for the pressure
37. portant for the process described here that there is a very uni form stable and controlled temperature environment enclosing the fixed point cell We have developed three designs of fixed point furnaces to satisfy these requirements The Model 9114 furnace has three independent heaters and con trollers designed to be used for a temperature range up to 680 C as shown in Figure 3 22 6 Realization of the Freezing Point Maintaining the cell with argon 6 4 The Model 9115 furnace with a sodium in inconel heat pipe is designed for a temperature range from 500 C through 1000 C Although the heat pipe can be used up to 1100 C as a safety precaution it is suggested not to use the Model 9115 furnace above 1000 C for a long period of time Figure 4 The Model 9116 furnace is designed with a special single zone heater for the freezing point of copper 1084 62 C The furnaces and their temperature uni formities are listed in Table 6 Table 6 The furnaces for fixed points and their temperature uniformity Temperature Fixed Point The Equipment Used Uniformity The freezing point of indium Model 9114 furnace three zones 0 02 C The freezing point of tin Model 9114 furnace three zones 0 02 C The freezing point of zinc Model 9114 furnace three zones 0 02 C The freezing point of aluminum Model 9114 furnace three zones 0 03 C The freezing point of aluminum Model 9115 furnace heat pipe 0 03 C The freezing point
38. t of them to approxi mately 80 mm Put a piece of graphite disk into the outer shell on the top of pure fused silica wool disks Push down the graphite disk until the height of pure fused silica wool disks decreases to approximately 40 mm using Pyrex tube and fused silica well as tools Keep the surface of fused silica well clean during the entire assembling process the fused silica well will be assembled into the cell finally Insert the fused silica well through the holes of graphite disks and pure fused silica wool disks into the well of the crucible assembly to check the assembling Then take the fused silica well out of the outer shell Repeat steps 4 and 5 until five graphite disks and enough pure fused sil ica wool disks are assembled into the outer shell as shown in Figure 2 Carefully assemble the stainless steel SS cap onto the top of the cell fused silica outer shell as shown in Figure 2 Keep the outer surface of the fused silica cell clean to avoid devitrification Clean the outer surface of the cell and the cell support container basket before assembling the cell into the container Clean tissue and Reagent Grade alcohol can be used for the cleaning Put pure fused silica quartz glass wool felt with a thickness about 1 on the in ner bottom of the container as cushion Insert the cell into cell basket in the furnace 6 Realization of the Freezing Point Background Information 6 3 lt Purge Gas Con
39. ter the cell and SPRT are in the equi librium The first SPRT is at room temperature at the time of insertion The furnace temperature is kept at a stable temperature of 1 C below the freezing point 16 After all SPRTs are measured set the furnace temperature at 20 C with a rate of 2 C min 17 The cell should be pumped for 10 min in the second day At that time the furnace temperature should close to room temperature Fill pure ar gon to a pressure that is slightly higher than local atmosphere pressure Close all valves Turn the furnace power off 6 6 5 Realization of the freezing point of Ag 1 Start pumping by using a mechanical vacuum pump When the pressure 30 reaches approximately 1e 2 torr open the vacuum valve slowly If the pressure reaches approximately 1e 2 again it might take about 30 min 6 Realization of the Freezing Point Procedure for realizing the freeze In Zn Al Ag and Cu fixed points utes it indicates all connections and sealing are in good condition If not check all connections and sealing one by one Turn on the high vacuum system diffusion pump or molecular pump and open high vacuum valve to pump cell The vacuum should be at 1e 5 torr or lower Insert a high temperature SPRT into the reentrant well of the cell to mon itor the temperature of the cell Make sure the vertical temperature gradient of the furnace with the cell is good enough The furnace vertical temperature gradient shoul
40. to a minimum A long immersion depth of the thermometer into the liquid metal makes any error due to the thermal conductivity along the thermometer sheath and leads negligible 5 Care of Your Metal Freezing Point Cell General Information 5 1 5 2 Care of Your Metal Freezing Point Cell General Information The metal freezing point cell is an extremely delicate device Great care must be taken in handling using and transporting the cell The quartz outer shell is easily broken It is suggested that the cell be kept in the vertical position for safety although putting a cool cell in the horizontal orientation for a short time period will not cause any damage It is dangerous to transport the cell by gen eral carrier therefore the cell should be hand carried from one place to another place It is extremely important to keep the outer surface of the cell clean to avoid devitrification of the quartz Never touch the cell with bare hands Whenever you have to handle the cell always wear clean cotton gloves or use clean paper If there is any chance that the outside of the cell has been touched with bare hands clean the quartz with alcohol before inserting it into a furnace Devitrification of Quartz Glass Devitrification is a natural process with quartz glass materials Quartz is uti lized in a glass state The most stable state for quartz is crystalline Therefore devitrification is the tendency of the quartz g lass to return to
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