- Email: [email protected]
Apparatus for μSR and μLCR experiments on fluids at high pressure and temperature
ARTICLE IN PRESS
Physica B 374–375 (2006) 314–316 www.elsevier.com/locate/physb
Apparatus for mSR and mLCR experiments on fluids at high pressure and temperature Jean-Claude Brodovitch TRIUMF and Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6
Abstract Apparatus has been developed to perform mSR and mLCR experiments on aqueous solutions at high pressure and high temperature (up to 400 bar, 400 1C). The target sample container is a 30 ml cylinder constructed of titanium alloy, with walls thick enough to withstand these temperature and pressure conditions without distortion, fitted with a specially shaped front window, thin enough to allow backward muons to penetrate and stop completely in the sample volume without reaching the end of the cell. The target and its support have been designed: (1) to fit in the very constrained geometry of the bore of a superconducting magnet; and (2) such that even at the highest rated temperature of the sample, the temperature at the outside surface of the assembly is low enough to accept regular positron plastic scintillators positioned in very close proximity. In addition, the sample cell can be connected to an adjustable ballast volume to accomodate fluid sample expansion, and thus allow independent control of temperature and pressure. With the ability to obtain mLCR data under these temperature and pressure conditions, new radical signals observed by mSR during muon irradiation of acetone can now be assigned unambiguously. r 2005 Elsevier B.V. All rights reserved. PACS: 36.10.Dr; 82.33.De; 83.85.c Keywords: Muonium; High pressure; Radicals; Super-critical water
1. Introduction In addition to temperature, study of the effect of pressure on a chemical reaction can, in principle, provide valuable information on the transition state of the reaction, and this feature has been used for the study of some muonium reactions [1]. More generally, for aqueous medium around the water critical point (374 1C, 221 bar), some of the physical properties (like pK or dielectric constant) change very significantly, and pressure in combination with temperature can be tuned to determine or alter the outcome of a reaction. For organic aqueous systems this aspect has found application in very diverse area, from biology of hydrothermal vents to destruction of hazardous wastes. A good understanding of the physical and chemical processes taking place in these conditions requires a probe which can function in the harsh Tel.: +604 2913790; fax: +604 2913765.
E-mail address: [email protected]. 0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.11.084
environment of ‘‘high’’ temperature and pressure, preferably in real time. It is not trivial experimentally, since the reaction container must be built in such a way as to sustain the stress, yet permit application of an appropriate spectroscopic probe. The mechanisms of organic reactions in sub- or supercritical water involves free radical intermediates, and a program has been undertaken to use the muonium as a radical probe [1,2]. Muons are attractive in this context because: (1) they can penetrate a thick-walled vessel and stop in the fluid sample, and (2) the high-energy emitted positrons which convey the spectroscopic information can also penetrate the walls and be detected outside the container. In practical terms, to perform such an experiment, the requirements of the sample cell are the following:
Strength of the container: in the present case, must be able to withstand without deformation the stress generated by internal pressure of at least E250 bar at E400 1C.
ARTICLE IN PRESS J.-C. Brodovitch / Physica B 374–375 (2006) 314–316
Entrance window: must be as thin as possible to facilitate muon penetration with a minimum of scattering. Cell material: ideally, should be chemically inert.
Retaining Flange
Domed window
315
Body
Heater Coil
Sample out
All these requirements were met with the apparatus used for the studies described in Refs. [2–5]. However, due to its bulk, the sample cell could be used only in spectrometers with a very open magnet geometry. In particular, this precluded mLCR experiments, which are performed in high longitudinal magnetic field created by a superconducting solenoid with restricted geometry. At the same time, mLCR experiments are critical for the unambiguous characterization of muoniated radicals, which was the initial goal of the study and spurred the development of the high-pressure system described in this report. 2. Experimental
+ Thermocouple Sample in
Cell support
Water cooled jacket
50 mm Fig. 2. Scaled drawing of the high-temperature, high-pressure titanium cell showing various attachments.
+
Pressure transducer
Target
Experiments for this study were performed in the backward muon channel M9B at the TRIUMF cyclotron facility in Vancouver, Canada. The pressure cell was designed to be small enough to fit inside the same water-cooled vacuum jacket used for other experiments performed with the Helios superconducting magnet. In this instance, the ‘‘vacuum’’ jacket acts as a temperature shield between the hot cell (up to 400 1C) and the surrounding plastic scintillators. A constant gentle flow of air through the jacket serves as a cold source for good temperature control. The general assembly is shown in Fig. 1. The cell was machined out of a titanium alloy (Ti 6AL4 V), which is very inert chemically, has excellent strength property up to 500 1C and has relative low density. The entrance window is 2 mm thick (0.89 g/cm2) and 19 mm diameter; it has been machined in a dome shape for added strength. It is pressed into the cell opening by a titanium alloy flange bolted to the body of the cell by 12 high strength stainless-steel screws. The conical fitting of the window to the body insures proper sealing by a mismatched cone angle arrangement (581 cone of the window pressing into a 601 receiving cone). The volume of the cell is 30 ml. To flow the sample in or out, two openings have been machined at the back of the cell to accept 1/1600 capillary stainless-steel tubing (HPLC SSI fittings). A third opening accepts a thermocouple well (Swagelok fitting) to monitor the temperature in the center of the sample volume. A commercial heating element (Watlow) is wrapped noninductively around the body of the cell to control the temperature. A scaled diagram of the arrangement is shown in Fig. 2. High pressure cell
Cell support
Nitrogen purge line
Sample solution MHPV4 V6
Vacuum
V7 V5
V2A Spare
MHPV3
Sample
Hydraulic Fluid
Test Gauge Hydraulic hand pump
V5A Spare
Trap
Ballast/Pressure transmitter
Adjustable relif valve Release Valve
Fig. 3. Block diagram of high-pressure set-up; Vxx are low-pressure valves, HPVx and MHPVx are high-pressure valves.
Sample delivery/removal is achieved through a network of HPLC capillary stainless-steel tubing connected at one end to the sample storage container, and at the other end to a vacuum pump for removal of the spent sample; there is also the option to purge the system or to flush the sample out by flowing an inert gas. The sample volume is connected through capillary tubing to a variable buffer volume consisting of thin stainless-steel bellows immersed in the pressurizing hydraulic fluid. The bellows have the dual role of allowing for pressure control, while separating the sample from the hydraulic fluid. The bellows can expand to E30 ml. Pressure can be applied with a hydraulic hand pump (rated 30,000 bar) by ‘‘squeezing’’ the bellows; note that this arrangement can function only if the thin metal bellows are under isobaric conditions. To limit excess pressure, the system is fitted with an adjustable pressure leak valve attached to the hydraulic fluid side. A block diagram of the arrangement is shown in Fig. 3. 3. Results and discussion
100 mm Water cooled vacuum jacket Fig. 1. General assembly of the high-pressure cell support.
In a preliminary bench test, the system was filled with pure water and cycled several times through its stated maximum operating conditions (400 1C, 400 bar), checking
ARTICLE IN PRESS 316
J.-C. Brodovitch / Physica B 374–375 (2006) 314–316
for any permanent deformation of the cell. In tests with the beam, the fraction of incoming muons stopping in the sample volume compared favorably with previous arrangement. However, for sample density o0.5 g/cm2, the cell is too short to stop completely the muons before they reach the end of the cell. For a higher density sample, and with a muon beam collimated to 15 mm diameter, E11% of incoming muons stop in the body and front window of the cell; this was determined by irradiating the cell filled with water with 70 meV/c m, and measuring the fraction of the total asymmetry which shows a relaxation characteristic of m stopping in titanium [6]. In the most demanding temperature conditions encountered, the temperature of the jacket surface close to the scintillators does not exceed a safe 50 1C. The set-up presents two main drawbacks: (1) the plumbing consisting of thin capillaries is very sluggish to evacuate; (2) the bellows representing a dead-end cannot be emptied by simple flow-through, and have to be rinsed very carefully to ensure complete removal on the spent sample. Thus, changing sample and/or temperature can be a lengthy operation (1–2 h). We intend to construct a duplicate system which would speed up some operation by having one set-up collecting data, while the other, off-line, could be conditioned for another sample or temperature. The main advantage of the set-up is that its geometry is compatible with other sample holders used at TRIUMF with the Helios superconductor solenoid, and does not required a special counter arrangement. In addition, the attached plumbing consisting of the thin capillary is quite flexible and allows the assembly to be moved in or out of the muon beam easily. This arrangement (high-pressure set-up/Helios/M9B) was originally designed to gather mLCR data in the longitudinal field provided by Helios. Although the TRIUMF M9B beam line was designed to provide a longitudinally polarized muon beam, a special tune was developed to offer a polarization with a major perpendicular component (65–70%). With this feature, just by changing the beam line ‘‘tune’’ both type of data (TFmSR and mLCR) can be collected without disturbing the cell and sample arrangement.
4. Conclusion An apparatus has been designed to perform routinely TFmSR and mLCR experiments in conditions covering the critical point of water. In particular, this added mLCR capability has been successfully used to confirm unambiguously that the new radical observed previously by TFmSR [7] during muon irradiation of an aqueous solution of acetone at high temperature is due to addition of Mu to the enol form of acetone [8]. Other studies of radicals in this ‘‘hostile’’ environment are ongoing [9]. Acknowledgements We thank Paul Percival and other members of the SFUMU group for encouragement, discussions and assistance with experiments; Donald Arseneau for his ‘‘metal bellows’’ idea and for development of beam tunes; the staff of the Centre for Molecular and Materials Science at TRIUMF for technical support; and Jess Brewer for kindly providing the m data used to characterize the cell. This research was financially supported by the Natural Sciences and Engineering Research Council of Canada and, through TRIUMF, by the National Research Council of Canada. References [1] J.-C. Brodovitch, S.-K. Leung, P.W. Percival, D. Yu, K.E. Newman, Radiat. Phys. Chem. 32 (1988) 105. [2] P.W. Percival, J.-C. Brodovitch, K. Ghandi, B. Addison-Jones, J. Schu¨th, D. Bartels, Phys. Chem. Chem. Phys. 1 (1999) 4999. [3] K. Ghandi, J.-C. Brodovitch, B. Addison-Jones, P.W. Percival, I. McKenzie, Physica B 289–290 (2000) 476. [4] K. Ghandi, B. Addison-Jones, J.-C. Brodovitch, I. McKenzie, P.W. Percival, J. Schu¨th, Phys. Chem. Chem. Phys. 4 (2002) 586. [5] K. Ghandi, B. Addison-Jones, J.-C. Brodovitch, S. Kecman, P.W. Percival, J. Schu¨th, Physica B 326 (2003) 55. [6] J.H. Brewer, Private communication (2005). [7] K. Ghandi, B. Addison-Jones, J.-C. Brodovitch, B.M. McCollum, I. McKenzie, P.W. Percival, J. Am. Chem. Soc. 125 (2003) 9594. [8] P.W. Percival, J.-C. Brodovitch, K. Ghandi, B.M. McCollum, I. McKenzie, J. Am. Chem. Soc. 127 (2005) 13714. [9] P.W. Percival, J.-C. Brodovitch, K. Ghandi, B.M. McCollum, I. McKenzie, Organic free radicals in supercritical water, presentation O21, MuSR2005 Conference, Oxford, UK, August 2005.
Physica B 374–375 (2006) 314–316 www.elsevier.com/locate/physb
Apparatus for mSR and mLCR experiments on fluids at high pressure and temperature Jean-Claude Brodovitch TRIUMF and Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6
Abstract Apparatus has been developed to perform mSR and mLCR experiments on aqueous solutions at high pressure and high temperature (up to 400 bar, 400 1C). The target sample container is a 30 ml cylinder constructed of titanium alloy, with walls thick enough to withstand these temperature and pressure conditions without distortion, fitted with a specially shaped front window, thin enough to allow backward muons to penetrate and stop completely in the sample volume without reaching the end of the cell. The target and its support have been designed: (1) to fit in the very constrained geometry of the bore of a superconducting magnet; and (2) such that even at the highest rated temperature of the sample, the temperature at the outside surface of the assembly is low enough to accept regular positron plastic scintillators positioned in very close proximity. In addition, the sample cell can be connected to an adjustable ballast volume to accomodate fluid sample expansion, and thus allow independent control of temperature and pressure. With the ability to obtain mLCR data under these temperature and pressure conditions, new radical signals observed by mSR during muon irradiation of acetone can now be assigned unambiguously. r 2005 Elsevier B.V. All rights reserved. PACS: 36.10.Dr; 82.33.De; 83.85.c Keywords: Muonium; High pressure; Radicals; Super-critical water
1. Introduction In addition to temperature, study of the effect of pressure on a chemical reaction can, in principle, provide valuable information on the transition state of the reaction, and this feature has been used for the study of some muonium reactions [1]. More generally, for aqueous medium around the water critical point (374 1C, 221 bar), some of the physical properties (like pK or dielectric constant) change very significantly, and pressure in combination with temperature can be tuned to determine or alter the outcome of a reaction. For organic aqueous systems this aspect has found application in very diverse area, from biology of hydrothermal vents to destruction of hazardous wastes. A good understanding of the physical and chemical processes taking place in these conditions requires a probe which can function in the harsh Tel.: +604 2913790; fax: +604 2913765.
E-mail address: [email protected]. 0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.11.084
environment of ‘‘high’’ temperature and pressure, preferably in real time. It is not trivial experimentally, since the reaction container must be built in such a way as to sustain the stress, yet permit application of an appropriate spectroscopic probe. The mechanisms of organic reactions in sub- or supercritical water involves free radical intermediates, and a program has been undertaken to use the muonium as a radical probe [1,2]. Muons are attractive in this context because: (1) they can penetrate a thick-walled vessel and stop in the fluid sample, and (2) the high-energy emitted positrons which convey the spectroscopic information can also penetrate the walls and be detected outside the container. In practical terms, to perform such an experiment, the requirements of the sample cell are the following:
Strength of the container: in the present case, must be able to withstand without deformation the stress generated by internal pressure of at least E250 bar at E400 1C.
ARTICLE IN PRESS J.-C. Brodovitch / Physica B 374–375 (2006) 314–316
Entrance window: must be as thin as possible to facilitate muon penetration with a minimum of scattering. Cell material: ideally, should be chemically inert.
Retaining Flange
Domed window
315
Body
Heater Coil
Sample out
All these requirements were met with the apparatus used for the studies described in Refs. [2–5]. However, due to its bulk, the sample cell could be used only in spectrometers with a very open magnet geometry. In particular, this precluded mLCR experiments, which are performed in high longitudinal magnetic field created by a superconducting solenoid with restricted geometry. At the same time, mLCR experiments are critical for the unambiguous characterization of muoniated radicals, which was the initial goal of the study and spurred the development of the high-pressure system described in this report. 2. Experimental
+ Thermocouple Sample in
Cell support
Water cooled jacket
50 mm Fig. 2. Scaled drawing of the high-temperature, high-pressure titanium cell showing various attachments.
+
Pressure transducer
Target
Experiments for this study were performed in the backward muon channel M9B at the TRIUMF cyclotron facility in Vancouver, Canada. The pressure cell was designed to be small enough to fit inside the same water-cooled vacuum jacket used for other experiments performed with the Helios superconducting magnet. In this instance, the ‘‘vacuum’’ jacket acts as a temperature shield between the hot cell (up to 400 1C) and the surrounding plastic scintillators. A constant gentle flow of air through the jacket serves as a cold source for good temperature control. The general assembly is shown in Fig. 1. The cell was machined out of a titanium alloy (Ti 6AL4 V), which is very inert chemically, has excellent strength property up to 500 1C and has relative low density. The entrance window is 2 mm thick (0.89 g/cm2) and 19 mm diameter; it has been machined in a dome shape for added strength. It is pressed into the cell opening by a titanium alloy flange bolted to the body of the cell by 12 high strength stainless-steel screws. The conical fitting of the window to the body insures proper sealing by a mismatched cone angle arrangement (581 cone of the window pressing into a 601 receiving cone). The volume of the cell is 30 ml. To flow the sample in or out, two openings have been machined at the back of the cell to accept 1/1600 capillary stainless-steel tubing (HPLC SSI fittings). A third opening accepts a thermocouple well (Swagelok fitting) to monitor the temperature in the center of the sample volume. A commercial heating element (Watlow) is wrapped noninductively around the body of the cell to control the temperature. A scaled diagram of the arrangement is shown in Fig. 2. High pressure cell
Cell support
Nitrogen purge line
Sample solution MHPV4 V6
Vacuum
V7 V5
V2A Spare
MHPV3
Sample
Hydraulic Fluid
Test Gauge Hydraulic hand pump
V5A Spare
Trap
Ballast/Pressure transmitter
Adjustable relif valve Release Valve
Fig. 3. Block diagram of high-pressure set-up; Vxx are low-pressure valves, HPVx and MHPVx are high-pressure valves.
Sample delivery/removal is achieved through a network of HPLC capillary stainless-steel tubing connected at one end to the sample storage container, and at the other end to a vacuum pump for removal of the spent sample; there is also the option to purge the system or to flush the sample out by flowing an inert gas. The sample volume is connected through capillary tubing to a variable buffer volume consisting of thin stainless-steel bellows immersed in the pressurizing hydraulic fluid. The bellows have the dual role of allowing for pressure control, while separating the sample from the hydraulic fluid. The bellows can expand to E30 ml. Pressure can be applied with a hydraulic hand pump (rated 30,000 bar) by ‘‘squeezing’’ the bellows; note that this arrangement can function only if the thin metal bellows are under isobaric conditions. To limit excess pressure, the system is fitted with an adjustable pressure leak valve attached to the hydraulic fluid side. A block diagram of the arrangement is shown in Fig. 3. 3. Results and discussion
100 mm Water cooled vacuum jacket Fig. 1. General assembly of the high-pressure cell support.
In a preliminary bench test, the system was filled with pure water and cycled several times through its stated maximum operating conditions (400 1C, 400 bar), checking
ARTICLE IN PRESS 316
J.-C. Brodovitch / Physica B 374–375 (2006) 314–316
for any permanent deformation of the cell. In tests with the beam, the fraction of incoming muons stopping in the sample volume compared favorably with previous arrangement. However, for sample density o0.5 g/cm2, the cell is too short to stop completely the muons before they reach the end of the cell. For a higher density sample, and with a muon beam collimated to 15 mm diameter, E11% of incoming muons stop in the body and front window of the cell; this was determined by irradiating the cell filled with water with 70 meV/c m, and measuring the fraction of the total asymmetry which shows a relaxation characteristic of m stopping in titanium [6]. In the most demanding temperature conditions encountered, the temperature of the jacket surface close to the scintillators does not exceed a safe 50 1C. The set-up presents two main drawbacks: (1) the plumbing consisting of thin capillaries is very sluggish to evacuate; (2) the bellows representing a dead-end cannot be emptied by simple flow-through, and have to be rinsed very carefully to ensure complete removal on the spent sample. Thus, changing sample and/or temperature can be a lengthy operation (1–2 h). We intend to construct a duplicate system which would speed up some operation by having one set-up collecting data, while the other, off-line, could be conditioned for another sample or temperature. The main advantage of the set-up is that its geometry is compatible with other sample holders used at TRIUMF with the Helios superconductor solenoid, and does not required a special counter arrangement. In addition, the attached plumbing consisting of the thin capillary is quite flexible and allows the assembly to be moved in or out of the muon beam easily. This arrangement (high-pressure set-up/Helios/M9B) was originally designed to gather mLCR data in the longitudinal field provided by Helios. Although the TRIUMF M9B beam line was designed to provide a longitudinally polarized muon beam, a special tune was developed to offer a polarization with a major perpendicular component (65–70%). With this feature, just by changing the beam line ‘‘tune’’ both type of data (TFmSR and mLCR) can be collected without disturbing the cell and sample arrangement.
4. Conclusion An apparatus has been designed to perform routinely TFmSR and mLCR experiments in conditions covering the critical point of water. In particular, this added mLCR capability has been successfully used to confirm unambiguously that the new radical observed previously by TFmSR [7] during muon irradiation of an aqueous solution of acetone at high temperature is due to addition of Mu to the enol form of acetone [8]. Other studies of radicals in this ‘‘hostile’’ environment are ongoing [9]. Acknowledgements We thank Paul Percival and other members of the SFUMU group for encouragement, discussions and assistance with experiments; Donald Arseneau for his ‘‘metal bellows’’ idea and for development of beam tunes; the staff of the Centre for Molecular and Materials Science at TRIUMF for technical support; and Jess Brewer for kindly providing the m data used to characterize the cell. This research was financially supported by the Natural Sciences and Engineering Research Council of Canada and, through TRIUMF, by the National Research Council of Canada. References [1] J.-C. Brodovitch, S.-K. Leung, P.W. Percival, D. Yu, K.E. Newman, Radiat. Phys. Chem. 32 (1988) 105. [2] P.W. Percival, J.-C. Brodovitch, K. Ghandi, B. Addison-Jones, J. Schu¨th, D. Bartels, Phys. Chem. Chem. Phys. 1 (1999) 4999. [3] K. Ghandi, J.-C. Brodovitch, B. Addison-Jones, P.W. Percival, I. McKenzie, Physica B 289–290 (2000) 476. [4] K. Ghandi, B. Addison-Jones, J.-C. Brodovitch, I. McKenzie, P.W. Percival, J. Schu¨th, Phys. Chem. Chem. Phys. 4 (2002) 586. [5] K. Ghandi, B. Addison-Jones, J.-C. Brodovitch, S. Kecman, P.W. Percival, J. Schu¨th, Physica B 326 (2003) 55. [6] J.H. Brewer, Private communication (2005). [7] K. Ghandi, B. Addison-Jones, J.-C. Brodovitch, B.M. McCollum, I. McKenzie, P.W. Percival, J. Am. Chem. Soc. 125 (2003) 9594. [8] P.W. Percival, J.-C. Brodovitch, K. Ghandi, B.M. McCollum, I. McKenzie, J. Am. Chem. Soc. 127 (2005) 13714. [9] P.W. Percival, J.-C. Brodovitch, K. Ghandi, B.M. McCollum, I. McKenzie, Organic free radicals in supercritical water, presentation O21, MuSR2005 Conference, Oxford, UK, August 2005.