From The College of Engineering At The Pennsylvania State University: “Scientists identify new mechanism of corrosion”


From The College of Engineering


Penn State Bloc

The Pennsylvania State University

Ashley WennersHerron

Molten salt corroded a metal barrier, appearing disconnected on a slice view of the damage (right). Researchers imaged the corrosion in 3D and reconstructed the path the salt took through metal (left). Credit: Yang Yang/Penn State. All Rights Reserved.

Controlling one-dimensional wormhole corrosion could help advance power plant designs.

It started with a mystery: How did molten salt breach its metal container? Understanding the behavior of molten salt, a proposed coolant for next-generation nuclear reactors and fusion power, is a question of critical safety for advanced energy production. The multi-institutional research team, co-led by Penn State, initially imaged a cross-section of the sealed container, finding no clear pathway for the salt appearing on the outside. The researchers then used electron tomography, a 3D imaging technique, to reveal the tiniest of connected passages linking two sides of the solid container. That finding only led to more questions for the team investigating the strange phenomenon.

They published the answers today (Feb. 22) in Nature Communications [below].

Corrosion, a ubiquitous failure mode of materials, is traditionally measured in three dimensions or two dimensions, but those theories were not sufficient to explain the phenomenon in this case,” said co-corresponding author Yang Yang, assistant professor of engineering science and mechanics and of nuclear engineering at Penn State. He is also affiliated with the National Center for Electron Microscopy at The DOE’s Lawrence Berkeley National Laboratory, as well as the Materials Research Institute at Penn State. “We found that this penetrating corrosion was so localized, it only existed in one dimension — like a wormhole.

Wormholes on Earth, unlike the hypothetical astrophysical phenomenon, are typically bored by insects like worms and beetles. They dig into the ground, wood or fruits, leaving one hole behind as they excavate an unseen labyrinth. The worm may return to the surface through a new hole. From the surface, it looks like the worm disappears at one point in space and time and reappears at another. Electron tomography could reveal the hidden tunnels of the molten salt’s route on a microscopic scale whose morphology looks very similar to the wormholes.

To interrogate how the molten salt “digs” through metal, Yang and the team developed new tools and analysis approaches. According to Yang, their findings not only uncover a new mechanism of corrosion morphology, but also point to the potential of intentionally designing such structures to enable more advanced materials.

“Corrosion is often accelerated at specific sites due to various material defects and distinct local environments, but the detection, prediction and understanding of localized corrosion is extremely challenging,” said co-corresponding author Andrew M. Minor, professor of materials science and engineering at the University of California Berkeley and Lawrence Berkeley National Laboratory.

The team hypothesized that wormhole formation is linked to the exceptional concentration of vacancies — the empty sites that result from removing atoms — in the material. To prove this, the team combined 4D scanning transmission electron microscopy with theoretical calculations to identify the vacancies in the material. Together, this allowed the researchers to map vacancies in the atomic arrangement of the material at the nanometer scale. The resulting resolution is 10,000 times higher than conventional detection methods, Yang said.

Materials are not perfect,” said co-corresponding author Michael Short, associate professor of nuclear science and engineering at the Massachusetts Institute of Technology (MIT). “They have vacancies, and the vacancy concentration increases as the material is heated, is irradiated or, in our case, undergoes corrosion. Typical vacancy concentrations are much less than the one caused by molten salt, which aggregates and serve as the precursor of the wormhole.

Molten salt, which can be used as a reaction medium for materials synthesis, recycling solvent and more in addition to a nuclear reactor coolant, selectively removes atoms from the material during corrosion, forming the 1D wormholes along 2D defects, called grain boundaries, in the metal. The researchers found that molten salt filled the voids of various metal alloys in unique ways.

Only after we know how the salt infiltrates can we intentionally control or use it,” said co-first author Weiyue Zhou, postdoctoral associate at MIT. “This is crucial for the safety of many advanced engineering systems.

Now that the researchers better understand how the molten salt traverses specific metals — and how it changes depending on the salt and metal types — they said they hope to apply that physics to better predict the failure of materials and design more resistant materials.

“As a next step, we want to understand how this process evolves as a function of time and how we can capture the phenomenon with simulation to help understand the mechanisms,” said co-author Mia Jin, assistant professor of nuclear engineering at Penn State. “Once modeling and experiments can go hand-in-hand, it can be more efficient to learn how to make new materials to suppress this phenomenon when undesired and utilize it otherwise.”

Other contributors include co-authors Jim Ciston, M.C. Scott, Sheng Yin, Qin Yu, Robert O. Ritchie and Mark Asta, The DOE’s Lawrence Berkeley National Laboratory; co-authors Mingda Li and Ju Li, MIT; Sarah Y. Wang, Ya-Qian Zhang and Steven E. Zeltmann, University of California-Berkeley; Matthew J. Olszta and Daniel K. Schreiber, The DOE’s Pacific Northwest National Laboratory; and John R. Scully, University of Virginia. Minor, Scott, Ritchie and Asta are also affiliated with the University of California-Berkeley.

This work was primarily supported by FUTURE (Fundamental Understanding of Transport Under Reactor Extremes), an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Basic Energy Sciences.

Fig. 1: Differences between 3D, 2D, and 1D corrosion.
All corrosion occurs in a top-down manner, i.e., the penetration direction through thickness is from −z to +z. a Schematic drawing of a typical bulk bicontinuous dealloying corrosion morphology. b Schematic drawing of a typical pitting corrosion morphology with the volume set as transparent. The grain boundaries (GBs) were not displayed because both intergranular and intragranular pitting can occur. c Schematic drawing of a typical intergranular corrosion morphology with the volume set as opaque. The sides of the cube display the cross-sectional views. d Schematic drawing of 1D wormhole corrosion in a polycrystalline material. The upper half is a cross-sectional view showing discontinuous dots (i.e., voids filled by molten salt) along the GBs. The bottom half is a volumetric cutaway along the GBs where the 1D percolating network of tunnels on the grain surfaces is clearly shown in red. The dark blue color in a to c indicates free space such as cracks, voids, crevices etc., while the red color in d indicates wormholes filled with molten salt. e A representative false-colored SEM image showing the cross-section of Ni-20Cr after corrosion. f FIB-SEM 3D reconstruction of the volume shown in (e). The dimension of the box is 6.6 μm (x) × 3.5 μm (y) × 4.1 μm (z).

Fig. 2: Evidence of 1D wormhole corrosion and preferential etching/corrosion along one side of the grain boundary (GB).
The primary salt penetration/corrosion direction is along the z axis. a FIB-SEM 3D reconstruction of a much larger volume in a Ni-20Cr sample after molten salt corrosion. b A single-slice view showing discontinuous voids along GBs. c STEM HAADF image and EDX chemical mapping depicting elemental distributions from a thin (<100 nm) slice of the GB corrosion microstructure on a representative Ni-20Cr sample.

Nature Communications

See the full article here .

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The Penn State College of Engineering is the engineering school of the Pennsylvania State University, headquartered at the University Park campus in University Park, Pennsylvania. It was established in 1896, under the leadership of George W. Atherton. Today, with 13 academic departments and degree programs, over 11,000 enrolled undergraduate and graduate students (8,166 at the University Park campus, and 3,059 at other campuses), and research expenditures of $124 million for the 2016-2017 academic year, the Penn State College of Engineering is one of the leading engineering schools in the United States. It is estimated that at least one out of every fifty engineers in the United States got their bachelor’s degree from Penn State.

The appointment of George Atherton as president in 1882 created an era of extraordinary stability and growth for Penn State. Top priority was given to enlarging the engineering program, and Atherton immediately approved an equipment expenditure of $3,000 for practicums and laboratory sessions. Atherton held strongly to the view that Penn State should be an engineering and industrial institution, rather than a classical one, and that classics should not be a “leading object” in a college curriculum. The logical conclusion of this was that mechanic arts were also to be placed on par with agriculture, given the rapid industrialization of the nation. All students now took identical coursework during their freshman and sophomore years, with a specialization in engineering reserved for their junior and senior years.

Additionally, short courses (three in agriculture, one in chemistry, one in mining, and one in elementary mechanics) began to be offered, with no admission or degree requirements.

Despite the improvements to the civil engineering curriculum, Atherton knew that further evolution was needed. To that end, he challenged Louis Reber, a mathematics instructor, to attend The Massachusetts Institute of Technology for graduate work in mechanical engineering – and to pay particular attention to the processes and procedures used for engineering education – in order to develop Penn State’s two-year mechanic arts program into a four-year mechanical engineering curriculum. Reber took to the challenge, and also studied engineering education methods in use at Worcester Polytechnic Institute, Stevens Institute of Technology, Washington University in St. Louis, and The University of Minnesota to establish a baseline for Penn State’s program, which at that time consisted of mechanical drawing, woodworking, and carpentry. Reber also supervised the installation of a forge and foundry, and in 1884 asked for $3,500 to construct new building solely devoted to mechanic arts; Atherton immediately approved Reber’s request, and the resulting building was the first structure erected for purely academic purposes. Machinery and equipment for the building were purchased at reduced prices from equipment manufacturers based on the advertising potential and inherent goodwill to be found in labeling items “for educational purposes.”

In addition to providing instruction, the mechanical engineering department also managed the pumphouse, steam heating plant, and (beginning in 1887) the fifty-horsepower steam engine and generator used to power the incandescent lighting at the campus. The students thus gained practical experience via the chores required to manage and maintain these machines. The creation of the mechanical engineering curriculum segregated students into “general” and “technical” paths (not entirely dissimilar to modern-day general education and major-specific instruction requirements), and the curriculum featured what is now considered “typical” coursework in science and mathematics, as well as several practicums (one for each of the fall, winter, and spring terms) to develop skills such as drawing, pattern making, surveying, chemistry, mechanics, forging, and machine construction.

Thornton Osmond also issued recommendations that electrical engineering be spun off into its own field (it had previously resided in the physics department); Atherton approved this request, and the Department of Physics and Electrotechnics was created in 1887 to explore the practical applications of electricity. The revised engineering curricula proved popular: of the 92 students enrolled for the 1887-88 academic year, over 35% were in engineering (18 mechanical, 15 civil). The subsequent year’s enrollment rose to 113, of which 42% in engineering (22 mechanical, 17 civil, 9 electrical).

The growing popularity of the engineering curricula also required physical growth of the campus. In 1891, $100,000 was allotted to construct a building devoted entirely to engineering. This building, named Main Engineering, was dedicated on February 22, 1893, with most of the dedication speech focused on the importance of an engineering education to national prosperity and progress. Additional machinery, including Allis-Chalmers triple-expansion steam engine (extensively modified for laboratory instruction and experimentation), was purchased and installed. The engineering program continued to expand its offerings: in 1893, the trustees approved the addition of a course in mining engineering, with Magnus C. Ihlseng (formerly of The Colorado School of Mines) named professor and department head. Electrical engineering fully split from Physics and Electrotechnics, becoming its own department headed by John Price Jackson –who, at age 24, is easily the youngest department head on campus. By 1890, Main Engineering housed four engineering departments (civil, mechanical, mining, and electrical) in space originally intended for two. Increases in enrollment remained unceasing: in the 1890-91 academic year there were 127 undergraduates, 73 of which are in engineering (37 civil, 19 mechanical, 17 electrotechnical); by 1893, this had increased to 181 students, 128 in engineering (57 electrical, 44 mechanical, 18 civil, 9 mining). Needless to say, the overcrowding became problematic.

Coursework expansions were also underway. The department of civil engineering began to include instruction in sanitary and hydraulic engineering; however, students still did not yet have the opportunity to specialize in specific facet of desired profession outside of lab and thesis work. In 1894, a new curriculum requirement was added: all freshmen, sophomore, and junior engineering students were required to take a two-week summer course to gain field experience via visits to coal mines, railroad shops, foundries, power stations, and similar businesses. This marked the first offering of a summer session in Penn State history.

The increasing demand led to the formation of seven schools within Penn State. The Second Morrill Act (1890) gave each land-grant institution $15,000, which increased at a rate of $1,000 per year (to a maximum of $25,000), to be invested in instruction in agriculture, mechanic arts, etc. with “specific reference to their applications in the industry of life.” Engineering absorbed most of the at the expense of development of non-technical curricula. Atherton remained convinced that the college should increase instruction in liberal studies for all students, to become “[men] of broad culture and good citizen[s].” To that end, the establishment of the seven schools was intended to eliminate duplication of instruction and resources while also encouraging and facilitating cooperation among related departments. Perhaps most importantly, it also shifted the burden of administration from the president’s office onto the deans. Louis Reber became the first dean of the school of engineering, which exercised authority over the civil, mechanical, and electrical engineering departments. The mining engineering curriculum formed the core for the School of Mines, with Magnus Ihlseng named as dean.

Penn State Campus

The The Pennsylvania State University is a public state-related land-grant research university with campuses and facilities throughout Pennsylvania. Founded in 1855 as the Farmers’ High School of Pennsylvania, Penn State became the state’s only land-grant university in 1863. Today, Penn State is a major research university which conducts teaching, research, and public service. Its instructional mission includes undergraduate, graduate, professional and continuing education offered through resident instruction and online delivery. In addition to its land-grant designation, it also participates in the sea-grant, space-grant, and sun-grant research consortia; it is one of only four such universities (along with Cornell University, Oregon State University, and University of Hawaiʻi at Mānoa). Its University Park campus, which is the largest and serves as the administrative hub, lies within the Borough of State College and College Township. It has two law schools: Penn State Law, on the school’s University Park campus, and Dickinson Law, in Carlisle. The College of Medicine is in Hershey. Penn State is one university that is geographically distributed throughout Pennsylvania. There are 19 commonwealth campuses and 5 special mission campuses located across the state. The University Park campus has been labeled one of the “Public Ivies,” a publicly funded university considered as providing a quality of education comparable to those of the Ivy League.
The Pennsylvania State University is a member of The Association of American Universities an organization of American research universities devoted to maintaining a strong system of academic research and education.

Annual enrollment at the University Park campus totals more than 46,800 graduate and undergraduate students, making it one of the largest universities in the United States. It has the world’s largest dues-paying alumni association. The university offers more than 160 majors among all its campuses.

Annually, the university hosts the Penn State IFC/Panhellenic Dance Marathon (THON), which is the world’s largest student-run philanthropy. This event is held at the Bryce Jordan Center on the University Park campus. The university’s athletics teams compete in Division I of the NCAA and are collectively known as the Penn State Nittany Lions, competing in the Big Ten Conference for most sports. Penn State students, alumni, faculty and coaches have received a total of 54 Olympic medals.

Early years

The school was sponsored by the Pennsylvania State Agricultural Society and founded as a degree-granting institution on February 22, 1855, by Pennsylvania’s state legislature as the Farmers’ High School of Pennsylvania. The use of “college” or “university” was avoided because of local prejudice against such institutions as being impractical in their courses of study. Centre County, Pennsylvania, became the home of the new school when James Irvin of Bellefonte, Pennsylvania, donated 200 acres (0.8 km2) of land – the first of 10,101 acres (41 km^2) the school would eventually acquire. In 1862, the school’s name was changed to the Agricultural College of Pennsylvania, and with the passage of the Morrill Land-Grant Acts, Pennsylvania selected the school in 1863 to be the state’s sole land-grant college. The school’s name changed to the Pennsylvania State College in 1874; enrollment fell to 64 undergraduates the following year as the school tried to balance purely agricultural studies with a more classic education.

George W. Atherton became president of the school in 1882, and broadened the curriculum. Shortly after he introduced engineering studies, Penn State became one of the ten largest engineering schools in the nation. Atherton also expanded the liberal arts and agriculture programs, for which the school began receiving regular appropriations from the state in 1887. A major road in State College has been named in Atherton’s honor. Additionally, Penn State’s Atherton Hall, a well-furnished and centrally located residence hall, is named not after George Atherton himself, but after his wife, Frances Washburn Atherton. His grave is in front of Schwab Auditorium near Old Main, marked by an engraved marble block in front of his statue.

Early 20th century

In the years that followed, Penn State grew significantly, becoming the state’s largest grantor of baccalaureate degrees and reaching an enrollment of 5,000 in 1936. Around that time, a system of commonwealth campuses was started by President Ralph Dorn Hetzel to provide an alternative for Depression-era students who were economically unable to leave home to attend college.

In 1953, President Milton S. Eisenhower, brother of then-U.S. President Dwight D. Eisenhower, sought and won permission to elevate the school to university status as The Pennsylvania State University. Under his successor Eric A. Walker (1956–1970), the university acquired hundreds of acres of surrounding land, and enrollment nearly tripled. In addition, in 1967, the Penn State Milton S. Hershey Medical Center, a college of medicine and hospital, was established in Hershey with a $50 million gift from the Hershey Trust Company.

Modern era

In the 1970s, the university became a state-related institution. As such, it now belongs to the Commonwealth System of Higher Education. In 1975, the lyrics in Penn State’s alma mater song were revised to be gender-neutral in honor of International Women’s Year; the revised lyrics were taken from the posthumously-published autobiography of the writer of the original lyrics, Fred Lewis Pattee, and Professor Patricia Farrell acted as a spokesperson for those who wanted the change.

In 1989, the Pennsylvania College of Technology in Williamsport joined ranks with the university, and in 2000, so did the Dickinson School of Law. The university is now the largest in Pennsylvania. To offset the lack of funding due to the limited growth in state appropriations to Penn State, the university has concentrated its efforts on philanthropy.


Penn State is classified among “R1: Doctoral Universities – Very high research activity”. Over 10,000 students are enrolled in the university’s graduate school (including the law and medical schools), and over 70,000 degrees have been awarded since the school was founded in 1922.

Penn State’s research and development expenditure has been on the rise in recent years. For fiscal year 2013, according to institutional rankings of total research expenditures for science and engineering released by the National Science Foundation , Penn State stood second in the nation, behind only Johns Hopkins University and tied with the Massachusetts Institute of Technology , in the number of fields in which it is ranked in the top ten. Overall, Penn State ranked 17th nationally in total research expenditures across the board. In 12 individual fields, however, the university achieved rankings in the top ten nationally. The fields and sub-fields in which Penn State ranked in the top ten are materials (1st), psychology (2nd), mechanical engineering (3rd), sociology (3rd), electrical engineering (4th), total engineering (5th), aerospace engineering (8th), computer science (8th), agricultural sciences (8th), civil engineering (9th), atmospheric sciences (9th), and earth sciences (9th). Moreover, in eleven of these fields, the university has repeated top-ten status every year since at least 2008. For fiscal year 2011, the National Science Foundation reported that Penn State had spent $794.846 million on R&D and ranked 15th among U.S. universities and colleges in R&D spending.

For the 2008–2009 fiscal year, Penn State was ranked ninth among U.S. universities by the National Science Foundation, with $753 million in research and development spending for science and engineering. During the 2015–2016 fiscal year, Penn State received $836 million in research expenditures.

The Applied Research Lab (ARL), located near the University Park campus, has been a research partner with the Department of Defense since 1945 and conducts research primarily in support of the United States Navy. It is the largest component of Penn State’s research efforts statewide, with over 1,000 researchers and other staff members.

The Materials Research Institute was created to coordinate the highly diverse and growing materials activities across Penn State’s University Park campus. With more than 200 faculty in 15 departments, 4 colleges, and 2 Department of Defense research laboratories, MRI was designed to break down the academic walls that traditionally divide disciplines and enable faculty to collaborate across departmental and even college boundaries. MRI has become a model for this interdisciplinary approach to research, both within and outside the university. Dr. Richard E. Tressler was an international leader in the development of high-temperature materials. He pioneered high-temperature fiber testing and use, advanced instrumentation and test methodologies for thermostructural materials, and design and performance verification of ceramics and composites in high-temperature aerospace, industrial, and energy applications. He was founding director of the Center for Advanced Materials (CAM), which supported many faculty and students from the College of Earth and Mineral Science, the Eberly College of Science, the College of Engineering, the Materials Research Laboratory and the Applied Research Laboratories at Penn State on high-temperature materials. His vision for Interdisciplinary research played a key role in creating the Materials Research Institute, and the establishment of Penn State as an acknowledged leader among major universities in materials education and research.

The university was one of the founding members of the Worldwide Universities Network (WUN), a partnership that includes 17 research-led universities in the United States, Asia, and Europe. The network provides funding, facilitates collaboration between universities, and coordinates exchanges of faculty members and graduate students among institutions. Former Penn State president Graham Spanier is a former vice-chair of the WUN.

The Pennsylvania State University Libraries were ranked 14th among research libraries in North America in the 2003–2004 survey released by The Chronicle of Higher Education. The university’s library system began with a 1,500-book library in Old Main. In 2009, its holdings had grown to 5.2 million volumes, in addition to 500,000 maps, five million microforms, and 180,000 films and videos.

The university’s College of Information Sciences and Technology is the home of CiteSeerX, an open-access repository and search engine for scholarly publications. The university is also the host to the Radiation Science & Engineering Center, which houses the oldest operating university research reactor. Additionally, University Park houses the Graduate Program in Acoustics, the only freestanding acoustics program in the United States. The university also houses the Center for Medieval Studies, a program that was founded to research and study the European Middle Ages, and the Center for the Study of Higher Education (CSHE), one of the first centers established to research postsecondary education.