Preface

The purpose of the book series Developments in Surface Contamination and Cleaning is to provide a continuous state-of-the-art critical look at the current knowledge of the behavior of both film-type and particulate surface contaminants. The first 8 volumes, published in 2008, 2010, 2011, 2012, 2013 (Volumes 5 and 6), 2015 (Volumes 7 and 8), and 2016 (2nd edition of the first volume), respectively, covered various topics dealing with the fundamental nature of contaminants, their measurement and characterization, and different techniques for their removal. Volume 9 is in production and is expected to be in print at the end of 2016. This book is the 10th volume in the series.

The individual contributions in this book provide state-of-the-art reviews by subject matter experts on types of contaminants and their behavior and contamination resources.

Metallic contaminants are ubiquitous as discrete particles or in ionic form. Even in very low concentrations, they can adversely affect the performance of high-end devices. The chapter by Rajiv Kohli provides an overview of the sources and generation of metallic contaminants and discusses some of their impacts. Analytical techniques are briefly described that are available to detect and characterize metallic contaminants at the nanoscale.

Babak Nasr, Suresh Dhaniyala and Goodarz Ahmadi present an overview of theoretical models for particle resuspension and the available experimental data on particle removal. The different particle removal models are described in detail and the important effects of surface roughness on particle detachment are described. A series of experimental data for particle resuspension in wind tunnel studies available in the literature was compiled, presented in terms of critical shear velocities, and compared against each other. Differences in the measured critical velocities for particle resuspension were observed that were attributed to different factors such as particle size, surface roughness, relative humidity, and the time duration that the surface was exposed to airflow. The theoretically predicted critical shear velocities for detachment of particles were compared with the available experimental data. The smooth surface contact models are seen to overestimate the critical shear velocity for particle removal. However, with the inclusion of effects of surface roughness, the model predictions were found to be in reasonable agreement with the data.

Drug substances and drug products are used for treating various diseases to save the lives of human beings. In their review, S. Lakshmana Prabu, T.N.K. Suriyaprakash, K. Ruckmani and R. Thirumurugan focus on good manufacturing practice (GMP) guidelines for preparation/manufacturing of drug substances and drug products. Drug substances and drug products should be manufactured using clean equipment with appropriate quality and in good environmental conditions to avoid contamination of the product and to produce the desired therapeutic effect. Effort should be made to build quality into the product during each stage of the manufacturing process rather than simply testing the product at the end. To regulate the manufacturing process, regulatory agencies along with pharmaceutical industrial organizations developed manufacturing guidelines that are reflected as GMP guidelines for the preparation/manufacturing of the drug substance and drug products. Various GMP guidelines are followed in respective regions in the world even though the fundamentals of all the guidelines remain the same. The GMP guidelines consist of various processes including quality management, personnel, personal hygiene and qualification, building and facilities, sanitation, documentation and records, material management, production and in-process controls, packaging and labeling of drug substances and drug products, storage and distribution, laboratory controls, validation, rejection and reuse of materials, complaints and recalls, and change control. Clean equipment, cleanrooms, and environmental conditions are critical process parameters to be monitored strictly in the manufacturing process to ensure the highest standard of quality and purity of the product with desired safety and efficacy of the drug product to meet the regulatory requirements.

The chapter by Barbara Kanegsberg and Ed Kanegsberg focuses on the rationale and utility of standards, the processes of writing and approval, and working with standards that are inconsistent or in conflict. Several organizations and groups involved in developing standards are highlighted. The information and ideas provided can be used for developing and revising standards and to improve the effectiveness in interpreting, utilizing, and managing standards. The utility of standards depends on the expertise of the people involved in developing those standards.

Surface cleaning is becoming increasingly important in modern manufacturing. Traditional cleaning processes are predominantly thermal processes and may not be applicable for the next generation of devices, which include parts manufactured at the micro/nanoscale that are sensitive to heat and abrasion. This problem with such parts can be overcome by a new surface cleaning technique called droplet-assisted laser cleaning (DALC). DALC uses a Q-switched Nd:YAG laser to vaporize a stream of water droplets to produce a succession of impacting shock waves at the surface of the component of interest. The generated shock waves can be used for various material processing applications, including removal of contaminants. The process exploits the combined potential of laser shock cleaning and optohydrodynamic processing through explosive vaporization of water droplets. In their contribution, José Manuel López López, Sundar Marimuthu and Alhaji M. Kamara discuss traditional laser cleaning processes from direct beam/contaminant interaction to laser shock cleaning (LSC). The DALC process discussed in this chapter was specifically designed to induce explosive vaporization of a 300-μm water droplet above the contaminated substrate surface. The shock pressure magnitude was analyzed using high-precision force and acceleration sensors. The effects of laser energy, number of pulses per position, gap distance, and scanning speed on the cleaning performance were investigated in detail. A contaminated substrate with micropolystyrene particles was used to evaluate the performance of the DALC system, and the results, in comparison to those obtained from the traditional laser shock cleaning process, show that DALC can be an excellent alternative to the existing laser-based cleaning process (ablation and shock).

We would like to express our heartfelt thanks to all the authors in this book for their contributions, enthusiasm, and cooperation. Our sincere appreciation goes to our publishers Kattie Washington, Christina Gifford, and Matthew Deans, who have strongly supported publication of this volume, in particular, and this series, in general. Melissa Read and the editorial staff at Elsevier have been instrumental in seeing the book to publication. Rajiv Kohli would also like to thank the staff of the STI library at the Johnson Space Center for their efforts in helping to locate obscure and difficult-to-access reference materials.