Diffraction

Diffraction-based techniques are best described as being super microscopes that can ‘see’ and ‘feel’ atomic phenomena without disruption or modification of the materials being investigated.

By probing crystalline matter with X-ray or neutron beams, and precisely measuring the angle at which the scattered beams interfere constructively (diffraction), novel aspects are studied directly at the atomic level in a non-destructive way.

These powerful probes directly visualise the microstructure of crystalline matter at the atomic level (10^-10 m sizes) to provide information that cannot be seen with even the most powerful microscopes available today.

Whilst the methodologies of X-ray and neutron diffraction are similar, their different interaction mechanisms (electromagnetic versus nuclear) and scattering properties with matter provide complementary information: X-Rays are suited for near-surface analysis, whilst neutrons, having substantially larger penetration depths, are well suited for bulk and depth-resolved analyses, as well as magnetic interactions.

This, in conjunction with the capability to enforce in situ changes in the sample environment, contributes substantially towards fundamental knowledge and understanding of matter.

The Diffraction facilities at Necsa are unique on the African continent with it being able to offer both X-ray and neutron diffraction based investigations at one institution.

These techniques provide fundamental insight into the crystallographic and/or magnetic order in materials that are of value to a plethora of scientific fields such as materials science, engineering (mechanical, metallurgical), chemistry, physics and geological sciences.

Necsa has (and is developing further) world-class beamline instruments to assist researchers from a wide range of disciplines to generate fundamental front-end knowledge as part of the National System of Innovation’s vision to boost SA’s knowledge economy and the IAEA’s vision to have an African regional Centre of Competence in Neutron Science at SAFARI-1.

This enables capabilities for advanced research, problem-solving and value addition to contributing to better understanding of processes and products.

The advanced research infrastructures are accessible for both academic and industrial projects.

Academic access is awarded on scientific merit following the review of a formal project proposal submission.

Many research projects are accommodated in conjunction with tertiary institutions in South Africa, as well as users from Africa.

Projects for industry and technology development initiatives are accommodated within contract research modalities.

The ability to study and understand materials fundamentally is key to the competitive innovations required to beneficiate our material resources into high-value export commodities.

Knowledge gained from the diffraction investigations enables cross-cutting value addition in industries involved in:

• New material’s developments
• New manufacturing techniques such as additive manufacture (3D printing), coatings, welds, etc.
• Validation of processes for performance enhancement techniques such as shot peening, laser peening, autofrettage, etc.
• Nuclear-related fuels, structural components and waste
• Alternative energy systems such as new generation batteries

World-class research infrastructure, expertise and know-how from highly skilled staff offer professional services in the following diffraction-related areas of application:

• Chemical phase analysis, both qualitative and quantitative
• Residual stress determination. X-rays enable near surface investigations whilst neutrons enable depth-resolved investigations
• Crystallographic texture analysis. X-rays enable determination of local texture whilst neutrons enable determination of global texture
• In-situ temperature dependent analyses of crystallographic phases and transitions
• In-situ temperature-dependent studies of magnetic ordering and phase transitions

Necsa has both X-ray and neutron diffraction instruments which performs residual stress and powder diffraction measurements.

The neutron powder diffraction instrument is extensively equipped for in-situ temperature studies covering the temperature range from 1.5 K to 1800 K.

Detailed descriptions of the instruments together with example applications are available at the following links:

Neutron Diffraction Facility (NDIFF):

• MPISI – Materials Probe for Internal Strain Investigations (http://www.necsa.co.za/mpisi)
• PITSI – Powder Instrument for Transition in Structure Investigations (http://www.necsa.co.za/pitsi)

X-ray diffraction lab:

• Bruker D8-Advance
• Bruker D8-Discover

The Diffraction section has close ties with a number of Higher Educational Institutions and staff routinely acts as lecturers, supervisors, co-supervisors and mentors to graduate and post-graduate students.

In 2016, Prof. Andrew Venter and the Diffraction section achieved finalist status with the National Science and Technology Forum (NSTF) awards in the category “Research leading to Innovation by a Corporate Organisation” for establishing the two world-class neutron diffraction instruments at the SAFARI-1 nuclear research reactor.

The honour was bestowed on South Africa to host the 9th International Conference on Mechanical Stress Evaluation by Neutron and Synchrotron Radiation (MECA SENS 2017) in 2017 and the Diffraction section of Necsa was appointed as the local organising committee.

The conference was extremely well received and attended by 95 delegates from 18 countries and 52 institutions.

The conference proceedings were published through Materials Research Forum, Millersville PA, USA and is available here (http://www.mrforum.com/product/mechanical-stress-evaluation/)

X-ray diffraction
Neutron diffraction
Chemical phase identification
Chemical phase quantification
Crystallographic phase transitions
Magnetic order
Magnetic phase transitions
Residual stress
Crystallographic texture