University of California Materials Research Neutron Diffractometer Project

HIPPO: HIgh Pressure - Preferred Orientation

We are delighted to report that the HIPPO diffractometer is finally installed and operational with limited functions. Ancillary equipment has not yet been interfaced. Presently there is a pause in beam delivery at LANSCE until June 2002. In summer and fall 2002 it should be possible to perform experiments. Please note that neither Kristin Bennett nor Bob von Dreele are continuing their careers as instrument scientists at Lujan and for any information about the present status of the facilities you should contact Alan Hurd ajhurd@lanl.gov.

Information and NEWS about Los Alamos can be obtained from this link.

If you wish to do neutron diffraction experiments at other facilities, contact neutron sources with similar diffractometers and users programs, among them:

• IPNS at Argonne National Laboratory
• ILL in Grenoble, France
• LLB at Saclay, France
• ISIS in United Kingdom
• FZ Juelich in Germany
• GKSS in Germany
• Chalk River in Canada
• JINR in Dubna, Russia

Conceptual design of HIPPO with T0 chopper, detector panels, sample chamber, and beam stop.

The HIPPO sample chamber under construction at Allied Technology, Alameda CA. Kristin Bennett, Rudy Wenk, Yanxia Xie and George Weber inspect it during final testing. 4.13.2000

Kristin Bennett loading a test sample (ammonite) on the automatic sample changer waiting for samples and neutrons at the Lujan Center.

Project Description

Recognizing that neutron diffraction offers some unique advantages for quantitative characterization of material properties, a consortium of University of California faculty and DOE National-Laboratory researchers, representing a broad range of disciplines, is building a novel time-of-flight (TOF) neutron diffractometer and associated equipment at the Los Alamos Neutron Science Center (LANSCE), under the auspices of the Department of Energy. DOE is funding this project through the BES program at approximately $4M. This instrument has been developed to satisfy the needs of the materials science community and should become available for testing in spring 2001 and for general use in summer 2001. Since two of its functions will be to subject materials to HIgh pressure and measure Preferred Orientation in polycrystals it has been given the acronym HIPPO but this does not exclude other applications.

The general goal is to build an instrument to investigate dynamic processes in heterogeneous bulk materials. A major limitation of neutrons has been the weak scattering. With HIPPO this problem is overcome by taking advantage of the improved source at LANSCE, a short flight path (flux at the sample: 10⁸ n cm^-2s^-1) and a novel three-dimensional arrangement of detectors covering a large surface area. The usual data collection time (days for high-pressure, hours for powders, textures, and temperatures) will be reduced to minutes (and even seconds), enabling us to study time-dependent processes in bulk samples with anisotropic properties. It is envisioned that HIPPO will attract ‘main-stream’ materials and earth scientists to neutron diffraction, which has so far been reserved for more specialized experiments. As a high throughput instrument, the new diffractometer will guarantee easy access and high availability. We anticipate that the number of investigations possible over the course of an 8-month annual running cycle will be 100-200, making neutron diffraction not only a method for a few dedicated specialists but also a viable resource for materials science community. While HIPPO will be part of the National user facility operated by LANSCE, the scientific program will be guided by the UCMRD consortium with the goal of satisfying national priorities and establishing an environment of scientific excellence. Proposals will be evaluated based on their scientific merit, the involvement of research groups in enhancing the facility and laboratory missions. With the vastly improved intensity and data acquisition systems, we envision a fast turnaround.

The core of the HIPPO design features a short initial flight path of 9m at Flight Path 4 of the the Lujan Center and an array of 1400 10atm ³He detector tubes covering more than 4.5m² with five detector banks at scattering angles ranging from backscattering (nominally 150° ) to low forward scattering (nominally 10° ). A T_o chopper removes the fast neutron prompt pulse. The collimation views a 12cm diameter round portion of a high intensity ambient water moderator, and converges to a maximum round beam size of 2 cm diameter at the sample position. For most applications samples ought to be fully immersed in the neutron beam and should not exceed this size. Smaller beam sizes at the sample position can be produced with adjustable collimation. It is anticipated that the count rate for some experiments will be approximately 20-60 times what is currently obtained on the present High Intensity Powder Diffractometer (HIPD), which will enable measurements in as little as 5-10s. The data acquisition will be based on current VME technology and make use of web-based visualization and control software. Experiments can be controlled remotely, e.g. from the laboratory of the user.

In a time-of-flight diffractometer each detector in a bank records a full d (time) spectrum. The different banks have different resolution (10° about 5%, 150° about 0.35%) and emphasize a different d-range (low angle banks high d-range, high angle banks low d-range). Different banks are therefore used in different applications. Most data obtained with the new diffractometer can be readily analyzed with existing software. Users can take processed data to their laboratories and process them on their PC with user-friendly existing GSAS or RITA Rietveld codes. Results are quickly reduced to a form that can be interpreted and published.

A large evacuated sample chamber (75 cm diameter cylinder) can accommodate various ancillary equipment such as cryostats and furnaces, pressure vessels and straining cells, goniometers, magnets and an automatic sample changer. With these capabilities in situ studies in a wide range of conditions can be performed. HIPPO will be used primarily for high pressure, texture, liquid/amorphous materials and reaction-kinetic studies.

The University of California Materials Research Diffractometer project aims at creating an instrument with easy access for mainstream materials scientists, including students.

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Advantages of Neutrons versus X-Rays and Electrons

HIPPO is not intended to compete with conventional methods but to make use of the unique properties of neutron diffraction. These include

• Low absorption / high penetration:
  bulk samples (not surfaces)
  large samples (coarse grained)
  environmental stages
  
• High spectral resolution:
  low symmetry materials (e.g. minerals, HTS, Pu)
  composites (rocks, metal matrix etc.)
  
• Scattering characteristics:
  Be, D, D₂O, Al-Si
  magnetic scattering

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Information from Diffraction Spectra of Bulk Materials

With TOF neutron diffraction each detector records a spectrum simultaneously. Depending on flight path, collimation geometry and Bragg angle, these spectra have good to excellent resolution and cover a wide d-range. In the case of HIPPO the specifications for different detector banks are:

Information from different detector banks can be combined.

Processing of neutron diffraction spectra has been greatly quantified and facilitated through application of the Rietveld technique and applying it to bulk materials. A wealth of information is contained in each spectrum. Some examples are:

• Peak position
  Lattice parameters
  

• Peak intensities:
  Crystal structure (atomic positions, temperature factors)
  Preferred orientation of polycrystals (texture)
  Phase proportions (of composites)
  

• Deviations from ideal peak positions:
  Internal stress (elastic strain)
  
• Peak shape:
  Microstructure (grain size, shape, defects)
  
• Peak asymmetry:
  Microstress
  

Several software packages exist to extract such information in an efficient and user-friendly manner. Two approaches are:

GSAS: Von Dreele R.B. (1997): Quantitative texture analysis by Rietveld refinement. J. Appl. Cryst. 30, 577-587.

MAUD: Lutterotti L., Matthies S., Wenk H.-R., Schultz A.J. and Richardson J.W. (1997): Combined texture and structure analysis of deformed limestone from time-of-flight neutron diffraction spectra. J. Appl. Phys. 81, 594-600.

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Ancillary Equipment (not yet interfaced!)

• 3-circle goniometer with kappa geometry

• 300-2000K gas flow furnace

• cryostat (5-270K)

• 20GPa-2000K high-pressure cell

• automatic sample changer with texture capabilities

• magnets

• straining goniometer (provided by the Technical University Hamburg-Harburg)

• special environments provided by users

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Some Research Applications

The HIPPO diffractometer can be applied in a wide variety of disciplines such as materials science and engineering, earth sciences, physics and chemistry. Examples of research include kinetics of reactions, high pressure investigations of complex systems with large sample volumes, intrinsic mechanical (texture and strain) and magnetic properties, texture evolution in polycrystals during deformation, recrystallization and phase transformations, preferred orientation and anisotropy of rocks (e.g. granite-mylonite, mantle peridotites), crystal structure of zeolites (Al-Si distribution, water), structure of liquids and melts (including Al-Si melts and glasses). It will be possible to perform dynamic experiments on bulk anisotropic samples at a wide range of temperature and pressure conditions.

Materials Science:

• Texture development during deformation and recrystallization (in situ)
• Phase transformations
• Texture and internal stresses in composites
• Reaction kinetics in ferroelectrics
• Phase transformations and texture development in high-temperature superconductors
• Phase transformations and textures in bulk Pu
• Texture analysis of Be (weak x-ray scattering)
• Structure of liquids and glasses
• Structure of polymers
• High pressure investigations

Earth Science:

• Structure of silicate melts
• Processes during curing of cement
• Phase relations and deformation of ice
• Preferred orientation and seismic anisotropy in deformed rocks
• Texture and ductility of salt
• Zeolite structures (Al-Si ordering, water)
• Amorphization by irradiation

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UCMRD Executive Committee

Kristin Bennett, LANSCE, LANL, Los Alamos, NM 87545
bennett@lanl.gov

John Bingert, MST-6, MS G770, Los Alamos, NM 87545
bingert@lanl.gov

Abhaya K. Datye, Dept. Chemical and Nuclear Engineering, UNM Albuquerque NM.
datye@unm.edu

Tony Habenschuss, Chemical and Analytical Science Div., MS 6197, Oak Ridge TN 37831-6201
habenschussa@ornl.gov

Alan Hurd, Lujan Center, LANL, Los Alamos, NM 87545
ajhurd@lanl.gov

Jean-Bernard Minster, IGPP, U.C. San Diego, CA 92093
jbminster@ucsd.edu

Mark Rodriguez, Sandia National Laboratories, ORG 1824, Albuquerque, 87185-5800
marodri@sandia.gov

James F. Shackelford, Dept. Chemical Engineering and Materials Science, U.C. Davis CA 95616
jfshackelford@ucdavis.edu

Hans-Rudolf Wenk, Dept. Earth and Planetary Science, U.C. Berkeley CA 94720
wenk@seismo.berkeley.edu

Workshops

• On Friday, October 29, 1999 a first HIPPO Workshop for the UC community was held at the Davis Campus under the auspices of Professor Jim Shackelford. 100 faculty and students from all UC Campuses participated at this event. The workshop was sponsored by the Los Alamos UCDRD program.

• A second workshop was held in Santa Fe February 28-March 2, 2001. Kristin Bennett did an outstanding job in arranging this meeting which attracted a wide range of participants from all over the world and many disciplines.

New Developments (1.28.2002)

• The automatic sample changer, the ILL heating cell, a 30GPa high pressure cell, and the kappa goniometer, and a straining cell (H. Mecking and H. Hartig) have been delivered. Lujan is in the process of programming them.
• We are happy to announce that a proposal for HIPPO user support has been approved. This grant called STONE will provide travel subsidies (up to $1000 per year) for students and faculty from UC Campuses and New Mexico Universities to visit Los Alamos for experiments (this subsidy also extends to UC and New Mexico users on other Lujan experiments).
• The Executive Committee and the SDT is formulating and negotiating a special HIPPO user program with LANSCE.
• Please be aware that the SNS (Spallation Neutron Source) Project at Oak Ridge is moving ahead and may become available in 2005. This will be a next generation of neutron instruments and we hope that HIPPO can prepare new users to take advantage of neutron diffraction and also to test instrument performance. John Parise at SUNY is spearheading high pressure beamlines at that facility and anyone interested should contact John jparise@notes.cc.sunysb.edu. The plan is to have a "second generation" HIPPO with higher intensity, higher resolution and larger sample chamber, suited for high pressure (500GPa), high temperature (10.000K), stress and strain.

Support for Faculty and Students from UC and New Mexico Universities

A program called STONE, with Los Alamos UCDRD and LANSCE support, is now in place to assist UC and New Mexico University users. It includes the following provisions:

• Travel subsidies (up to $1000 per year and up to $ 500 per experiment) for students and faculty from UC Campuses and New Mexico Universities to visit Los Alamos for experiments (this subsidy also extends to UC and New Mexico users on other Lujan instruments).
• Graduate or undergraduate student stipends to spend extended time (e.g. 3 months in summer) at LANSCE to conduct research in neutron diffraction.
• A one-year fellowship for a graduate student to engage in a PhD thesis project in materials or earth sciences that emphasizes the HIPPO diffractometer.
• Postdoctoral researcher to help users with data processing and data interpretation.

Open Positions

• We are looking for a postdoctoral scientist with some experience in neutron diffraction. The scientist will be maintaining contact and assist University users with data processing and data interpretation. He/she will also advance operating software and needs to have experience in computer programming (such as Fortran, C and Java). The candidate is expected to conduct a research program in materials science (or related field). We are particularly interested in modeling expertise for stress-strain interpretation and/or advancing structure analysis of amorphous materials.